This patchset fixes WLED's handling of enabled-strings: besides some
cleanup it is now actually possible to specify a non-contiguous array of
enabled strings (not necessarily starting at zero) and the values from
DT are now validated to prevent possible unexpected out-of-bounds
register and array element accesses.
Off-by-one mistakes in the maximum number of strings, also causing
out-of-bounds access, have been addressed as well.
Marijn Suijten (10):
backlight: qcom-wled: Pass number of elements to read to
read_u32_array
backlight: qcom-wled: Use cpu_to_le16 macro to perform conversion
backlight: qcom-wled: Override num-strings when enabled-strings is set
backlight: qcom-wled: Validate enabled string indices in DT
backlight: qcom-wled: Fix off-by-one maximum with default num_strings
backlight: qcom-wled: Remove unnecessary 4th default string in wled3
backlight: qcom-wled: Provide enabled_strings default for wled 4 and 5
backlight: qcom-wled: Remove unnecessary double whitespace
backlight: qcom-wled: Consistently use enabled-strings in
set_brightness
backlight: qcom-wled: Consider enabled_strings in autodetection
drivers/video/backlight/qcom-wled.c | 88 ++++++++++++++++++-----------
1 file changed, 55 insertions(+), 33 deletions(-)
--
2.33.0
of_property_read_u32_array takes the number of elements to read as last
argument. This does not always need to be 4 (sizeof(u32)) but should
instead be the size of the array in DT as read just above with
of_property_count_elems_of_size.
To not make such an error go unnoticed again the driver now bails
accordingly when of_property_read_u32_array returns an error.
Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
Signed-off-by: Marijn Suijten <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
---
drivers/video/backlight/qcom-wled.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index d094299c2a48..6af808af2328 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c
@@ -1528,11 +1528,18 @@ static int wled_configure(struct wled *wled)
string_len = of_property_count_elems_of_size(dev->of_node,
"qcom,enabled-strings",
sizeof(u32));
- if (string_len > 0)
- of_property_read_u32_array(dev->of_node,
+ if (string_len > 0) {
+ rc = of_property_read_u32_array(dev->of_node,
"qcom,enabled-strings",
wled->cfg.enabled_strings,
- sizeof(u32));
+ string_len);
+ if (rc) {
+ dev_err(dev, "Failed to read %d elements from "
+ "qcom,enabled-strings: %d\n",
+ string_len, rc);
+ return -EINVAL;
+ }
+ }
return 0;
}
--
2.33.0
When not specifying num-strings in the DT the default is used, but +1 is
added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
of 3 and 4 respectively, causing out of bounds reads and register
read/writes. This +1 exists for a deficiency in the DT parsing code,
and is simply omitted entirely - solving this oob issue - by allowing
one extra iteration of the wled_var_cfg function parsing this particular
property.
Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
Signed-off-by: Marijn Suijten <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
---
drivers/video/backlight/qcom-wled.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index 27e8949c7922..66ce77ee3099 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c
@@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
static u32 wled3_num_strings_values_fn(u32 idx)
{
- return idx + 1;
+ return idx;
}
static const struct wled_var_cfg wled3_num_strings_cfg = {
.fn = wled3_num_strings_values_fn,
- .size = 3,
+ .size = 4, /* [0, 3] */
};
static const struct wled_var_cfg wled4_num_strings_cfg = {
.fn = wled3_num_strings_values_fn,
- .size = 4,
+ .size = 5, /* [0, 4] */
};
static u32 wled3_switch_freq_values_fn(u32 idx)
@@ -1520,8 +1520,6 @@ static int wled_configure(struct wled *wled)
*bool_opts[i].val_ptr = true;
}
- cfg->num_strings = cfg->num_strings + 1;
-
string_len = of_property_count_elems_of_size(dev->of_node,
"qcom,enabled-strings",
sizeof(u32));
--
2.33.0
DT-bindings do not specify num-strings as mandatory property, yet it is
required to be specified even if enabled-strings is used. The length of
that property-array should already be enough to determine exactly which
and how many strings to enable.
Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
Signed-off-by: Marijn Suijten <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
---
drivers/video/backlight/qcom-wled.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index 9927ed98944a..29910e603c42 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c
@@ -1536,6 +1536,8 @@ static int wled_configure(struct wled *wled)
string_len, rc);
return -EINVAL;
}
+
+ cfg->num_strings = string_len;
}
return 0;
--
2.33.0
On Mon, Oct 04, 2021 at 09:27:32PM +0200, Marijn Suijten wrote:
> of_property_read_u32_array takes the number of elements to read as last
> argument. This does not always need to be 4 (sizeof(u32)) but should
> instead be the size of the array in DT as read just above with
> of_property_count_elems_of_size.
>
> To not make such an error go unnoticed again the driver now bails
> accordingly when of_property_read_u32_array returns an error.
>
> Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
> Signed-off-by: Marijn Suijten <[email protected]>
> Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Reviewed-by: Daniel Thompson <[email protected]>
> ---
> drivers/video/backlight/qcom-wled.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index d094299c2a48..6af808af2328 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -1528,11 +1528,18 @@ static int wled_configure(struct wled *wled)
> string_len = of_property_count_elems_of_size(dev->of_node,
> "qcom,enabled-strings",
> sizeof(u32));
> - if (string_len > 0)
> - of_property_read_u32_array(dev->of_node,
> + if (string_len > 0) {
> + rc = of_property_read_u32_array(dev->of_node,
> "qcom,enabled-strings",
> wled->cfg.enabled_strings,
> - sizeof(u32));
> + string_len);
> + if (rc) {
> + dev_err(dev, "Failed to read %d elements from "
> + "qcom,enabled-strings: %d\n",
> + string_len, rc);
> + return -EINVAL;
> + }
> + }
>
> return 0;
> }
> --
> 2.33.0
>
On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> When not specifying num-strings in the DT the default is used, but +1 is
> added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> of 3 and 4 respectively, causing out of bounds reads and register
> read/writes. This +1 exists for a deficiency in the DT parsing code,
> and is simply omitted entirely - solving this oob issue - by allowing
> one extra iteration of the wled_var_cfg function parsing this particular
> property.
>
> Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> Signed-off-by: Marijn Suijten <[email protected]>
> Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> ---
> drivers/video/backlight/qcom-wled.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index 27e8949c7922..66ce77ee3099 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
>
> static u32 wled3_num_strings_values_fn(u32 idx)
> {
> - return idx + 1;
> + return idx;
> }
>
> static const struct wled_var_cfg wled3_num_strings_cfg = {
> .fn = wled3_num_strings_values_fn,
> - .size = 3,
> + .size = 4, /* [0, 3] */
0 is not a valid value for this property.
> };
>
> static const struct wled_var_cfg wled4_num_strings_cfg = {
> .fn = wled3_num_strings_values_fn,
> - .size = 4,
> + .size = 5, /* [0, 4] */
Ditto.
> };
>
> static u32 wled3_switch_freq_values_fn(u32 idx)
> @@ -1520,8 +1520,6 @@ static int wled_configure(struct wled *wled)
> *bool_opts[i].val_ptr = true;
> }
>
> - cfg->num_strings = cfg->num_strings + 1;
> -
> string_len = of_property_count_elems_of_size(dev->of_node,
> "qcom,enabled-strings",
> sizeof(u32));
> --
> 2.33.0
>
On Mon, Oct 04, 2021 at 09:27:34PM +0200, Marijn Suijten wrote:
> DT-bindings do not specify num-strings as mandatory property, yet it is
> required to be specified even if enabled-strings is used. The length of
> that property-array should already be enough to determine exactly which
> and how many strings to enable.
>
> Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
> Signed-off-by: Marijn Suijten <[email protected]>
> Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Reviewed-by: Daniel Thompson <[email protected]>
On 2021-10-05 10:19:47, Daniel Thompson wrote:
> On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> > When not specifying num-strings in the DT the default is used, but +1 is
> > added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> > of 3 and 4 respectively, causing out of bounds reads and register
> > read/writes. This +1 exists for a deficiency in the DT parsing code,
> > and is simply omitted entirely - solving this oob issue - by allowing
> > one extra iteration of the wled_var_cfg function parsing this particular
> > property.
> >
> > Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> > Signed-off-by: Marijn Suijten <[email protected]>
> > Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> > ---
> > drivers/video/backlight/qcom-wled.c | 8 +++-----
> > 1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > index 27e8949c7922..66ce77ee3099 100644
> > --- a/drivers/video/backlight/qcom-wled.c
> > +++ b/drivers/video/backlight/qcom-wled.c
> > @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
> >
> > static u32 wled3_num_strings_values_fn(u32 idx)
> > {
> > - return idx + 1;
> > + return idx;
> > }
> >
> > static const struct wled_var_cfg wled3_num_strings_cfg = {
> > .fn = wled3_num_strings_values_fn,
> > - .size = 3,
> > + .size = 4, /* [0, 3] */
>
> 0 is not a valid value for this property.
These comments represent the possible loop iterations the DT "cfg
parser" runs through, starting at j=0 and running up until and including
j=3. Should I make that more clear or omit these comments entirely?
- Marijn
> > };
> >
> > static const struct wled_var_cfg wled4_num_strings_cfg = {
> > .fn = wled3_num_strings_values_fn,
> > - .size = 4,
> > + .size = 5, /* [0, 4] */
>
> Ditto.
>
>
> > };
> >
> > static u32 wled3_switch_freq_values_fn(u32 idx)
> > @@ -1520,8 +1520,6 @@ static int wled_configure(struct wled *wled)
> > *bool_opts[i].val_ptr = true;
> > }
> >
> > - cfg->num_strings = cfg->num_strings + 1;
> > -
> > string_len = of_property_count_elems_of_size(dev->of_node,
> > "qcom,enabled-strings",
> > sizeof(u32));
> > --
> > 2.33.0
> >
On Tue, Oct 05, 2021 at 12:06:06PM +0200, Marijn Suijten wrote:
> On 2021-10-05 10:19:47, Daniel Thompson wrote:
> > On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> > > When not specifying num-strings in the DT the default is used, but +1 is
> > > added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> > > of 3 and 4 respectively, causing out of bounds reads and register
> > > read/writes. This +1 exists for a deficiency in the DT parsing code,
> > > and is simply omitted entirely - solving this oob issue - by allowing
> > > one extra iteration of the wled_var_cfg function parsing this particular
> > > property.
> > >
> > > Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> > > Signed-off-by: Marijn Suijten <[email protected]>
> > > Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> > > ---
> > > drivers/video/backlight/qcom-wled.c | 8 +++-----
> > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > > index 27e8949c7922..66ce77ee3099 100644
> > > --- a/drivers/video/backlight/qcom-wled.c
> > > +++ b/drivers/video/backlight/qcom-wled.c
> > > @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
> > >
> > > static u32 wled3_num_strings_values_fn(u32 idx)
> > > {
> > > - return idx + 1;
> > > + return idx;
> > > }
> > >
> > > static const struct wled_var_cfg wled3_num_strings_cfg = {
> > > .fn = wled3_num_strings_values_fn,
> > > - .size = 3,
> > > + .size = 4, /* [0, 3] */
> >
> > 0 is not a valid value for this property.
>
> These comments represent the possible loop iterations the DT "cfg
> parser" runs through, starting at j=0 and running up until and including
> j=3. Should I make that more clear or omit these comments entirely?
The role of wled3_num_strings_values_fn() is to enumerate the list of
legal values for the property [ 1, 2, 3 ]. Your changes cause the
enumeration to include a non-legal value so that you can have an
identity mapping between the symbol and the enumerate value.
An alternative approach would be to leave the enumeration logic
alone but set the num_string default to UINT_MAX in all cases:
- cfg->num_strings = cfg->num_strings + 1;
+ if (cfg->num_strings == UINT_MAX)
+ cfg->num_strings =
+ else
+ /* Convert from enumerated to numeric form */
+ cfg->num_strings = wled3_num_strings_values_fn(
+ cfg->num_strings);
Daniel.
On Tue, Oct 05, 2021 at 11:38:43AM +0100, Daniel Thompson wrote:
> On Tue, Oct 05, 2021 at 12:06:06PM +0200, Marijn Suijten wrote:
> > On 2021-10-05 10:19:47, Daniel Thompson wrote:
> > > On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> > > > When not specifying num-strings in the DT the default is used, but +1 is
> > > > added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> > > > of 3 and 4 respectively, causing out of bounds reads and register
> > > > read/writes. This +1 exists for a deficiency in the DT parsing code,
> > > > and is simply omitted entirely - solving this oob issue - by allowing
> > > > one extra iteration of the wled_var_cfg function parsing this particular
> > > > property.
> > > >
> > > > Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> > > > Signed-off-by: Marijn Suijten <[email protected]>
> > > > Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> > > > ---
> > > > drivers/video/backlight/qcom-wled.c | 8 +++-----
> > > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > > > index 27e8949c7922..66ce77ee3099 100644
> > > > --- a/drivers/video/backlight/qcom-wled.c
> > > > +++ b/drivers/video/backlight/qcom-wled.c
> > > > @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
> > > >
> > > > static u32 wled3_num_strings_values_fn(u32 idx)
> > > > {
> > > > - return idx + 1;
> > > > + return idx;
>
>
> > > > }
> > > >
> > > > static const struct wled_var_cfg wled3_num_strings_cfg = {
> > > > .fn = wled3_num_strings_values_fn,
> > > > - .size = 3,
> > > > + .size = 4, /* [0, 3] */
> > >
> > > 0 is not a valid value for this property.
> >
> > These comments represent the possible loop iterations the DT "cfg
> > parser" runs through, starting at j=0 and running up until and including
> > j=3. Should I make that more clear or omit these comments entirely?
>
> The role of wled3_num_strings_values_fn() is to enumerate the list of
> legal values for the property [ 1, 2, 3 ]. Your changes cause the
> enumeration to include a non-legal value so that you can have an
> identity mapping between the symbol and the enumerate value.
>
> An alternative approach would be to leave the enumeration logic
> alone but set the num_string default to UINT_MAX in all cases:
>
> - cfg->num_strings = cfg->num_strings + 1;
> + if (cfg->num_strings == UINT_MAX)
> + cfg->num_strings =
Oops... looks like I missed the cfg->max_string_count here.
> + else
> + /* Convert from enumerated to numeric form */
> + cfg->num_strings = wled3_num_strings_values_fn(
> + cfg->num_strings);
PS the alternative option is not to treat num-strings as an enumerated
value at all and just read it directly without using wled_values()...
On 2021-10-05 11:53:12, Daniel Thompson wrote:
> On Tue, Oct 05, 2021 at 11:38:43AM +0100, Daniel Thompson wrote:
> > On Tue, Oct 05, 2021 at 12:06:06PM +0200, Marijn Suijten wrote:
> > > On 2021-10-05 10:19:47, Daniel Thompson wrote:
> > > > On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> > > > > When not specifying num-strings in the DT the default is used, but +1 is
> > > > > added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> > > > > of 3 and 4 respectively, causing out of bounds reads and register
> > > > > read/writes. This +1 exists for a deficiency in the DT parsing code,
> > > > > and is simply omitted entirely - solving this oob issue - by allowing
> > > > > one extra iteration of the wled_var_cfg function parsing this particular
> > > > > property.
> > > > >
> > > > > Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> > > > > Signed-off-by: Marijn Suijten <[email protected]>
> > > > > Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> > > > > ---
> > > > > drivers/video/backlight/qcom-wled.c | 8 +++-----
> > > > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > > > > index 27e8949c7922..66ce77ee3099 100644
> > > > > --- a/drivers/video/backlight/qcom-wled.c
> > > > > +++ b/drivers/video/backlight/qcom-wled.c
> > > > > @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
> > > > >
> > > > > static u32 wled3_num_strings_values_fn(u32 idx)
> > > > > {
> > > > > - return idx + 1;
> > > > > + return idx;
> > > > > }
> > > > >
> > > > > static const struct wled_var_cfg wled3_num_strings_cfg = {
> > > > > .fn = wled3_num_strings_values_fn,
> > > > > - .size = 3,
> > > > > + .size = 4, /* [0, 3] */
> > > >
> > > > 0 is not a valid value for this property.
> > >
> > > These comments represent the possible loop iterations the DT "cfg
> > > parser" runs through, starting at j=0 and running up until and including
> > > j=3. Should I make that more clear or omit these comments entirely?
> >
> > The role of wled3_num_strings_values_fn() is to enumerate the list of
> > legal values for the property [ 1, 2, 3 ]. Your changes cause the
> > enumeration to include a non-legal value so that you can have an
> > identity mapping between the symbol and the enumerate value.
> >
> > An alternative approach would be to leave the enumeration logic
> > alone but set the num_string default to UINT_MAX in all cases:
> >
> > - cfg->num_strings = cfg->num_strings + 1;
> > + if (cfg->num_strings == UINT_MAX)
> > + cfg->num_strings =
>
> Oops... looks like I missed the cfg->max_string_count here.
>
>
> > + else
> > + /* Convert from enumerated to numeric form */
> > + cfg->num_strings = wled3_num_strings_values_fn(
> > + cfg->num_strings);
>
>
> PS the alternative option is not to treat num-strings as an enumerated
> value at all and just read it directly without using wled_values()...
I much prefer doing that instead of trying to wrangle enumeration
parsing around integer values that are supposed to be used as-is. After
all this variable is already named to set the `+ 1` override currently,
and `qcom,enabled_strings` has "custom" handling as well. I'll extend
the validation to ensure num_strings>=1 too.
In addition, and this needs some investigation on the dt-bindings side
too, it might be beneficial to make both properties mutually exclusive.
When specifying qcom,enabled_strings it makes little sense to also
provide qcom,num_strings and we want the former to take precedence. At
that point one might ask why qcom,num_strings remains at all when DT can
use qcom,enabled_strings instead.
We will supposedly have to keep backwards compatibility with DTs in mind
so none of this can be removed or made mutually exclusive from a driver
standpoint, that all has to be done in dt-bindings yaml to be enforced
on checked-in DTs.
- Marijn
On Tue, Oct 05, 2021 at 01:44:35PM +0200, Marijn Suijten wrote:
> On 2021-10-05 11:53:12, Daniel Thompson wrote:
> > On Tue, Oct 05, 2021 at 11:38:43AM +0100, Daniel Thompson wrote:
> > > On Tue, Oct 05, 2021 at 12:06:06PM +0200, Marijn Suijten wrote:
> > > > On 2021-10-05 10:19:47, Daniel Thompson wrote:
> > > > > On Mon, Oct 04, 2021 at 09:27:36PM +0200, Marijn Suijten wrote:
> > > > > > When not specifying num-strings in the DT the default is used, but +1 is
> > > > > > added to it which turns wled3 into 4 and wled4/5 into 5 strings instead
> > > > > > of 3 and 4 respectively, causing out of bounds reads and register
> > > > > > read/writes. This +1 exists for a deficiency in the DT parsing code,
> > > > > > and is simply omitted entirely - solving this oob issue - by allowing
> > > > > > one extra iteration of the wled_var_cfg function parsing this particular
> > > > > > property.
> > > > > >
> > > > > > Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> > > > > > Signed-off-by: Marijn Suijten <[email protected]>
> > > > > > Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> > > > > > ---
> > > > > > drivers/video/backlight/qcom-wled.c | 8 +++-----
> > > > > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > > > > > index 27e8949c7922..66ce77ee3099 100644
> > > > > > --- a/drivers/video/backlight/qcom-wled.c
> > > > > > +++ b/drivers/video/backlight/qcom-wled.c
> > > > > > @@ -1255,17 +1255,17 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
> > > > > >
> > > > > > static u32 wled3_num_strings_values_fn(u32 idx)
> > > > > > {
> > > > > > - return idx + 1;
> > > > > > + return idx;
> > > > > > }
> > > > > >
> > > > > > static const struct wled_var_cfg wled3_num_strings_cfg = {
> > > > > > .fn = wled3_num_strings_values_fn,
> > > > > > - .size = 3,
> > > > > > + .size = 4, /* [0, 3] */
> > > > >
> > > > > 0 is not a valid value for this property.
> > > >
> > > > These comments represent the possible loop iterations the DT "cfg
> > > > parser" runs through, starting at j=0 and running up until and including
> > > > j=3. Should I make that more clear or omit these comments entirely?
> > >
> > > The role of wled3_num_strings_values_fn() is to enumerate the list of
> > > legal values for the property [ 1, 2, 3 ]. Your changes cause the
> > > enumeration to include a non-legal value so that you can have an
> > > identity mapping between the symbol and the enumerate value.
> > >
> > > An alternative approach would be to leave the enumeration logic
> > > alone but set the num_string default to UINT_MAX in all cases:
> > >
> > > - cfg->num_strings = cfg->num_strings + 1;
> > > + if (cfg->num_strings == UINT_MAX)
> > > + cfg->num_strings =
> >
> > Oops... looks like I missed the cfg->max_string_count here.
> >
> >
> > > + else
> > > + /* Convert from enumerated to numeric form */
> > > + cfg->num_strings = wled3_num_strings_values_fn(
> > > + cfg->num_strings);
> >
> >
> > PS the alternative option is not to treat num-strings as an enumerated
> > value at all and just read it directly without using wled_values()...
>
> I much prefer doing that instead of trying to wrangle enumeration
> parsing around integer values that are supposed to be used as-is. After
> all this variable is already named to set the `+ 1` override currently,
> and `qcom,enabled_strings` has "custom" handling as well. I'll extend
> the validation to ensure num_strings>=1 too.
Great.
> In addition, and this needs some investigation on the dt-bindings side
> too, it might be beneficial to make both properties mutually exclusive.
> When specifying qcom,enabled_strings it makes little sense to also
> provide qcom,num_strings and we want the former to take precedence.
If we are designing a "fix" for that then my view is that if both are
passed then num-strings should take precedence because it is an
explicit statement about the number of strings where enabled_strings
is implicit. In other words, if num-strings <= len(enabled_strings) then
we should do what we are told, otherwise report error.
> At that point one might ask why qcom,num_strings remains at all when
> DT can use qcom,enabled_strings instead. We will supposedly have to
> keep backwards compatibility with DTs in mind so none of this can be
> removed or made mutually exclusive from a driver standpoint, that all
> has to be done in dt-bindings yaml to be enforced on checked-in DTs.
So... perhaps I made a make offering a Reviewed-by: to a patch
that allows len(enabled-strings) to have precedence. If anything
currently uses enabled-strings then it *will* be 4 cells long and
is relying on num-strings to ensure the right things happens ;-) .
We'd like that case to keep working so we must allow num-strings to have
precedence. In other words, when you add the new code, please put it at
the end of the function!
Daniel.
>
> - Marijn
On 2021-10-05 15:03:49, Daniel Thompson wrote:
[..]
> > I much prefer doing that instead of trying to wrangle enumeration
> > parsing around integer values that are supposed to be used as-is. After
> > all this variable is already named to set the `+ 1` override currently,
> > and `qcom,enabled_strings` has "custom" handling as well. I'll extend
> > the validation to ensure num_strings>=1 too.
>
> Great.
>
>
> > In addition, and this needs some investigation on the dt-bindings side
> > too, it might be beneficial to make both properties mutually exclusive.
> > When specifying qcom,enabled_strings it makes little sense to also
> > provide qcom,num_strings and we want the former to take precedence.
>
> If we are designing a "fix" for that then my view is that if both are
> passed then num-strings should take precedence because it is an
> explicit statement about the number of strings where enabled_strings
> is implicit. In other words, if num-strings <= len(enabled_strings) then
> we should do what we are told, otherwise report error.
IMO both should be identical (num-strings == len(enabled-strings)) to
avoid ambiguity, but do read on.
> > At that point one might ask why qcom,num_strings remains at all when
> > DT can use qcom,enabled_strings instead. We will supposedly have to
> > keep backwards compatibility with DTs in mind so none of this can be
> > removed or made mutually exclusive from a driver standpoint, that all
> > has to be done in dt-bindings yaml to be enforced on checked-in DTs.
>
> So... perhaps I made a make offering a Reviewed-by: to a patch
> that allows len(enabled-strings) to have precedence. If anything
> currently uses enabled-strings then it *will* be 4 cells long and
> is relying on num-strings to ensure the right things happens ;-) .
Unfortunately Konrad (one of my team members) landed such a patch at the
beginning of this year because I failed to submit this patchset in time
while it has been sitting in my queue since 2019 after being used in a
downstream project. This is in pmi8994 which doesn't have anything
widely used / production ready yet, so I'd prefer to fix the DT instead
and remove / fix his comment:
/* Yes, all four strings *have to* be defined or things won't work. */
But this is mostly because, prior to this patchset, no default was set
for WLED4 so the 0'th string would get enabled num-strings (3 in
pmi8994's case) times.
Aside that there's only one more PMIC (also being worked on by
SoMainline) that sets qcom,enabled-strings: this is pm660l, pulled from
our local tree, and it actually has enabled-strings of length 2 which is
broken in its current form, exactly because of relying on this patchset.
Finally, we already discussed this inside SoMainline and the
number/enabled leds should most likely be moved out of the PMIC dtsi's
as they're probably panel, hence board or even device dependent.
> We'd like that case to keep working so we must allow num-strings to have
> precedence. In other words, when you add the new code, please put it at
> the end of the function!
Since there don't seem to be any substantial platforms/PMICs using this
functionality in a working manner, can I talk you into agreeing with
fixing the DT instead?
PS. In -next pmi8994_wled is only enabled for sony-xperia-tone, and
pm660l_wled has yet to be enabled by anything.
- Marijn
On Tue, Oct 05, 2021 at 05:23:26PM +0200, Marijn Suijten wrote:
> On 2021-10-05 15:03:49, Daniel Thompson wrote:
> [..]
> > > At that point one might ask why qcom,num_strings remains at all when
> > > DT can use qcom,enabled_strings instead. We will supposedly have to
> > > keep backwards compatibility with DTs in mind so none of this can be
> > > removed or made mutually exclusive from a driver standpoint, that all
> > > has to be done in dt-bindings yaml to be enforced on checked-in DTs.
> >
> > So... perhaps I made a make offering a Reviewed-by: to a patch
> > that allows len(enabled-strings) to have precedence. If anything
> > currently uses enabled-strings then it *will* be 4 cells long and
> > is relying on num-strings to ensure the right things happens ;-) .
>
> Unfortunately Konrad (one of my team members) landed such a patch at the
> beginning of this year because I failed to submit this patchset in time
> while it has been sitting in my queue since 2019 after being used in a
> downstream project. This is in pmi8994 which doesn't have anything
> widely used / production ready yet, so I'd prefer to fix the DT instead
> and remove / fix his comment:
>
> /* Yes, all four strings *have to* be defined or things won't work. */
>
> But this is mostly because, prior to this patchset, no default was set
> for WLED4 so the 0'th string would get enabled num-strings (3 in
> pmi8994's case) times.
>
> Aside that there's only one more PMIC (also being worked on by
> SoMainline) that sets qcom,enabled-strings: this is pm660l, pulled from
> our local tree, and it actually has enabled-strings of length 2 which is
> broken in its current form, exactly because of relying on this patchset.
>
> Finally, we already discussed this inside SoMainline and the
> number/enabled leds should most likely be moved out of the PMIC dtsi's
> as they're probably panel, hence board or even device dependent.
>
> > We'd like that case to keep working so we must allow num-strings to have
> > precedence. In other words, when you add the new code, please put it at
> > the end of the function!
>
> Since there don't seem to be any substantial platforms/PMICs using this
> functionality in a working manner, can I talk you into agreeing with
> fixing the DT instead?
I've no objections to seeing the DT updated. However I don't really see
what benefit we get from breaking existing DTs in order to do so.
"Cleaning up annoying legacy" is seldom a good reason to break existing
DTs since, if we could break DTs whenever we choose, there would never
be any annoying legacy to worry about. When conflicting properties
result in uninterpretable DTs then a break may be justified but that is
not the case here.
Daniel.
[snipping to not have the entire thread here]
> I've no objections to seeing the DT updated. However I don't really see
> what benefit we get from breaking existing DTs in order to do so.
>
> "Cleaning up annoying legacy" is seldom a good reason to break existing
> DTs since, if we could break DTs whenever we choose, there would never
> be any annoying legacy to worry about. When conflicting properties
> result in uninterpretable DTs then a break may be justified but that is
> not the case here.
>
>
> Daniel.
The only true user of wled as of right now is Xperia Tone platform,
which does not yet
have display support upstream, so unless one classifies lighting up an
otherwise black display
a dealbreaker, I think it'd be fine to bend the rules this time.
Konrad
On 2021-10-05 17:24:53, Daniel Thompson wrote:
> On Tue, Oct 05, 2021 at 05:23:26PM +0200, Marijn Suijten wrote:
> > On 2021-10-05 15:03:49, Daniel Thompson wrote:
> > [..]
> > > > At that point one might ask why qcom,num_strings remains at all when
> > > > DT can use qcom,enabled_strings instead. We will supposedly have to
> > > > keep backwards compatibility with DTs in mind so none of this can be
> > > > removed or made mutually exclusive from a driver standpoint, that all
> > > > has to be done in dt-bindings yaml to be enforced on checked-in DTs.
> > >
> > > So... perhaps I made a make offering a Reviewed-by: to a patch
> > > that allows len(enabled-strings) to have precedence. If anything
> > > currently uses enabled-strings then it *will* be 4 cells long and
> > > is relying on num-strings to ensure the right things happens ;-) .
> >
> > Unfortunately Konrad (one of my team members) landed such a patch at the
> > beginning of this year because I failed to submit this patchset in time
> > while it has been sitting in my queue since 2019 after being used in a
> > downstream project. This is in pmi8994 which doesn't have anything
> > widely used / production ready yet, so I'd prefer to fix the DT instead
> > and remove / fix his comment:
> >
> > /* Yes, all four strings *have to* be defined or things won't work. */
> >
> > But this is mostly because, prior to this patchset, no default was set
> > for WLED4 so the 0'th string would get enabled num-strings (3 in
> > pmi8994's case) times.
> >
> > Aside that there's only one more PMIC (also being worked on by
> > SoMainline) that sets qcom,enabled-strings: this is pm660l, pulled from
> > our local tree, and it actually has enabled-strings of length 2 which is
> > broken in its current form, exactly because of relying on this patchset.
> >
> > Finally, we already discussed this inside SoMainline and the
> > number/enabled leds should most likely be moved out of the PMIC dtsi's
> > as they're probably panel, hence board or even device dependent.
> >
> > > We'd like that case to keep working so we must allow num-strings to have
> > > precedence. In other words, when you add the new code, please put it at
> > > the end of the function!
> >
> > Since there don't seem to be any substantial platforms/PMICs using this
> > functionality in a working manner, can I talk you into agreeing with
> > fixing the DT instead?
>
> I've no objections to seeing the DT updated. However I don't really see
> what benefit we get from breaking existing DTs in order to do so.
>
> "Cleaning up annoying legacy" is seldom a good reason to break existing
> DTs since, if we could break DTs whenever we choose, there would never
> be any annoying legacy to worry about. When conflicting properties
> result in uninterpretable DTs then a break may be justified but that is
> not the case here.
As mentioned in my message and repeated by Konrad, the only "existing
DT" that could possibly be broken is a platform that's brought up by us
(SoMainline) and we're more than happy to improve the driver and leave
legacy DT behind us, unless there's more DT in circulation that hasn't
landed in Linux mainline but should be taken into account?
Anyway the plan is to leave qcom,num-strings in place so that the
default enabled_strings list in this driver actually serves a purpose.
Then, if num-strings and enabled-strings is provided the former has
precedence (assuming it doesn't exceed the size of the latter) but we'll
print a warning about this (now unnecessary) ambiguity, and if possible
at all - haven't found an example yet - make the properties mutually
exclusive in dt-bindings.
Disallowing both cases would only simplify the code in the end but we
can spend a few lines to support the desired legacy.
- Marijn
On Tue, Oct 05, 2021 at 07:34:00PM +0200, Marijn Suijten wrote:
> On 2021-10-05 17:24:53, Daniel Thompson wrote:
> > On Tue, Oct 05, 2021 at 05:23:26PM +0200, Marijn Suijten wrote:
> > > Since there don't seem to be any substantial platforms/PMICs using this
> > > functionality in a working manner, can I talk you into agreeing with
> > > fixing the DT instead?
> >
> > I've no objections to seeing the DT updated. However I don't really see
> > what benefit we get from breaking existing DTs in order to do so.
> >
> > "Cleaning up annoying legacy" is seldom a good reason to break existing
> > DTs since, if we could break DTs whenever we choose, there would never
> > be any annoying legacy to worry about. When conflicting properties
> > result in uninterpretable DTs then a break may be justified but that is
> > not the case here.
>
> As mentioned in my message and repeated by Konrad, the only "existing
> DT" that could possibly be broken is a platform that's brought up by us
> (SoMainline) and we're more than happy to improve the driver and leave
> legacy DT behind us, unless there's more DT in circulation that hasn't
> landed in Linux mainline but should be taken into account?
Devicetrees are supposed to be the domain of firmware (e.g. not part of
the kernel).
I'm therefore reluctant to adopt an "it only exists if it is upstream"
approach for documented DT bindings. Doubly so when it is our bugs that
causes DTs to be written in a manner which we then retrospectively
declare to be wrong.
> Anyway the plan is to leave qcom,num-strings in place so that the
> default enabled_strings list in this driver actually serves a purpose.
> Then, if num-strings and enabled-strings is provided the former has
> precedence (assuming it doesn't exceed the size of the latter) but
> we'll print a warning about this (now unnecessary) ambiguity, and if
> possible at all - haven't found an example yet - make the properties
> mutually exclusive in dt-bindings.
>
> Disallowing both cases would only simplify the code in the end but we
> can spend a few lines to support the desired legacy.
Yes, warning is OK for me.
Daniel.
On 2021-10-06 15:44:44, Daniel Thompson wrote:
> On Tue, Oct 05, 2021 at 07:34:00PM +0200, Marijn Suijten wrote:
> > On 2021-10-05 17:24:53, Daniel Thompson wrote:
> > > On Tue, Oct 05, 2021 at 05:23:26PM +0200, Marijn Suijten wrote:
> > > > Since there don't seem to be any substantial platforms/PMICs using this
> > > > functionality in a working manner, can I talk you into agreeing with
> > > > fixing the DT instead?
> > >
> > > I've no objections to seeing the DT updated. However I don't really see
> > > what benefit we get from breaking existing DTs in order to do so.
> > >
> > > "Cleaning up annoying legacy" is seldom a good reason to break existing
> > > DTs since, if we could break DTs whenever we choose, there would never
> > > be any annoying legacy to worry about. When conflicting properties
> > > result in uninterpretable DTs then a break may be justified but that is
> > > not the case here.
> >
> > As mentioned in my message and repeated by Konrad, the only "existing
> > DT" that could possibly be broken is a platform that's brought up by us
> > (SoMainline) and we're more than happy to improve the driver and leave
> > legacy DT behind us, unless there's more DT in circulation that hasn't
> > landed in Linux mainline but should be taken into account?
>
> Devicetrees are supposed to be the domain of firmware (e.g. not part of
> the kernel).
>
> I'm therefore reluctant to adopt an "it only exists if it is upstream"
> approach for documented DT bindings. Doubly so when it is our bugs that
> causes DTs to be written in a manner which we then retrospectively
> declare to be wrong.
I'm aware that DT is considered firmware and is ""intended"" to be
shipped separately (and probably only once out of the factory) but it
seems so far there's an advantage in updating DT in parallel with the
kernel. However this is the first time hearing that having dt-bindings
documentation available contributes to considering the DT contract
(more) stable. Either way I'd expect these bindings to have been fixed
much sooner if it was really actively used.
> > Anyway the plan is to leave qcom,num-strings in place so that the
> > default enabled_strings list in this driver actually serves a purpose.
> > Then, if num-strings and enabled-strings is provided the former has
> > precedence (assuming it doesn't exceed the size of the latter) but
> > we'll print a warning about this (now unnecessary) ambiguity, and if
> > possible at all - haven't found an example yet - make the properties
> > mutually exclusive in dt-bindings.
> >
> > Disallowing both cases would only simplify the code in the end but we
> > can spend a few lines to support the desired legacy.
>
> Yes, warning is OK for me.
Great, sending v2 shortly.
- Marijn