Add function of_pci_get_slot_power_limit(), which parses the
'slot-power-limit-milliwatt' DT property, returning the value in
milliwatts and in format ready for the PCIe Slot Capabilities Register.
Signed-off-by: Pali Rohár <[email protected]>
Signed-off-by: Marek Behún <[email protected]>
Reviewed-by: Rob Herring <[email protected]>
---
Changes in v2:
* Added support for PCIe 6.0 slot power limit encodings
* Round down slot power limit value
---
drivers/pci/of.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++
drivers/pci/pci.h | 15 +++++++++++
2 files changed, 79 insertions(+)
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index cb2e8351c2cc..549a404bd536 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -633,3 +633,67 @@ int of_pci_get_max_link_speed(struct device_node *node)
return max_link_speed;
}
EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);
+
+/**
+ * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
+ * property.
+ *
+ * @node: device tree node with the slot power limit information
+ * @slot_power_limit_value: pointer where the value should be stored in PCIe
+ * Slot Capabilities Register format
+ * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
+ * Slot Capabilities Register format
+ *
+ * Returns the slot power limit in milliwatts and if @slot_power_limit_value
+ * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
+ * scale in format used by PCIe Slot Capabilities Register.
+ *
+ * If the property is not found or is invalid, returns 0.
+ */
+u32 of_pci_get_slot_power_limit(struct device_node *node,
+ u8 *slot_power_limit_value,
+ u8 *slot_power_limit_scale)
+{
+ u32 slot_power_limit_mw;
+ u8 value, scale;
+
+ if (of_property_read_u32(node, "slot-power-limit-milliwatt",
+ &slot_power_limit_mw))
+ slot_power_limit_mw = 0;
+
+ /* Calculate Slot Power Limit Value and Slot Power Limit Scale */
+ if (slot_power_limit_mw == 0) {
+ value = 0x00;
+ scale = 0;
+ } else if (slot_power_limit_mw <= 255) {
+ value = slot_power_limit_mw;
+ scale = 3;
+ } else if (slot_power_limit_mw <= 255*10) {
+ value = slot_power_limit_mw / 10;
+ scale = 2;
+ } else if (slot_power_limit_mw <= 255*100) {
+ value = slot_power_limit_mw / 100;
+ scale = 1;
+ } else if (slot_power_limit_mw <= 239*1000) {
+ value = slot_power_limit_mw / 1000;
+ scale = 0;
+ } else if (slot_power_limit_mw <= 250*1000) {
+ value = 0xF0;
+ scale = 0;
+ } else if (slot_power_limit_mw <= 600*1000) {
+ value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25;
+ scale = 0;
+ } else {
+ value = 0xFF;
+ scale = 0;
+ }
+
+ if (slot_power_limit_value)
+ *slot_power_limit_value = value;
+
+ if (slot_power_limit_scale)
+ *slot_power_limit_scale = scale;
+
+ return slot_power_limit_mw;
+}
+EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 3d60cabde1a1..e10cdec6c56e 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -627,6 +627,9 @@ struct device_node;
int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
int of_get_pci_domain_nr(struct device_node *node);
int of_pci_get_max_link_speed(struct device_node *node);
+u32 of_pci_get_slot_power_limit(struct device_node *node,
+ u8 *slot_power_limit_value,
+ u8 *slot_power_limit_scale);
void pci_set_of_node(struct pci_dev *dev);
void pci_release_of_node(struct pci_dev *dev);
void pci_set_bus_of_node(struct pci_bus *bus);
@@ -653,6 +656,18 @@ of_pci_get_max_link_speed(struct device_node *node)
return -EINVAL;
}
+static inline u32
+of_pci_get_slot_power_limit(struct device_node *node,
+ u8 *slot_power_limit_value,
+ u8 *slot_power_limit_scale)
+{
+ if (slot_power_limit_value)
+ *slot_power_limit_value = 0;
+ if (slot_power_limit_scale)
+ *slot_power_limit_scale = 0;
+ return 0;
+}
+
static inline void pci_set_of_node(struct pci_dev *dev) { }
static inline void pci_release_of_node(struct pci_dev *dev) { }
static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
--
2.20.1
On Wed, Mar 02, 2022 at 03:57:32PM +0100, Pali Roh?r wrote:
> Add function of_pci_get_slot_power_limit(), which parses the
> 'slot-power-limit-milliwatt' DT property, returning the value in
> milliwatts and in format ready for the PCIe Slot Capabilities Register.
>
> Signed-off-by: Pali Roh?r <[email protected]>
> Signed-off-by: Marek Beh?n <[email protected]>
> Reviewed-by: Rob Herring <[email protected]>
> ---
> Changes in v2:
> * Added support for PCIe 6.0 slot power limit encodings
> * Round down slot power limit value
> ---
> drivers/pci/of.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 15 +++++++++++
> 2 files changed, 79 insertions(+)
>
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index cb2e8351c2cc..549a404bd536 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -633,3 +633,67 @@ int of_pci_get_max_link_speed(struct device_node *node)
> return max_link_speed;
> }
> EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);
> +
> +/**
> + * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
> + * property.
> + *
> + * @node: device tree node with the slot power limit information
> + * @slot_power_limit_value: pointer where the value should be stored in PCIe
> + * Slot Capabilities Register format
> + * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
> + * Slot Capabilities Register format
> + *
> + * Returns the slot power limit in milliwatts and if @slot_power_limit_value
> + * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
> + * scale in format used by PCIe Slot Capabilities Register.
> + *
> + * If the property is not found or is invalid, returns 0.
> + */
> +u32 of_pci_get_slot_power_limit(struct device_node *node,
> + u8 *slot_power_limit_value,
> + u8 *slot_power_limit_scale)
> +{
> + u32 slot_power_limit_mw;
> + u8 value, scale;
> +
> + if (of_property_read_u32(node, "slot-power-limit-milliwatt",
> + &slot_power_limit_mw))
> + slot_power_limit_mw = 0;
> +
> + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */
> + if (slot_power_limit_mw == 0) {
> + value = 0x00;
> + scale = 0;
> + } else if (slot_power_limit_mw <= 255) {
> + value = slot_power_limit_mw;
> + scale = 3;
> + } else if (slot_power_limit_mw <= 255*10) {
> + value = slot_power_limit_mw / 10;
> + scale = 2;
> + } else if (slot_power_limit_mw <= 255*100) {
> + value = slot_power_limit_mw / 100;
> + scale = 1;
> + } else if (slot_power_limit_mw <= 239*1000) {
> + value = slot_power_limit_mw / 1000;
> + scale = 0;
> + } else if (slot_power_limit_mw <= 250*1000) {
> + value = 0xF0;
> + scale = 0;
> + } else if (slot_power_limit_mw <= 600*1000) {
> + value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25;
> + scale = 0;
> + } else {
> + value = 0xFF;
> + scale = 0;
The purpose of this function is to return values that can be
programmed into the Slot Capabilities register. The 0xFF Slot Power
Limit Value is reserved, and I don't think we should use it until the
spec defines a meaning for it.
If the DT tells us 800W is available, we'll put 0xFF in Slot Power
Limit Value. If the spec eventually defines (0xFF, 0) to mean "1000W
available", a device may try to consume all 1000W, which will not
work.
If slot_power_limit_mw > 600*1000, I think we should advertise 600W
available (value 0xFE, scale 0) and return 600W (600*1000).
Bjorn
On Thursday 24 March 2022 12:13:37 Bjorn Helgaas wrote:
> On Wed, Mar 02, 2022 at 03:57:32PM +0100, Pali Rohár wrote:
> > Add function of_pci_get_slot_power_limit(), which parses the
> > 'slot-power-limit-milliwatt' DT property, returning the value in
> > milliwatts and in format ready for the PCIe Slot Capabilities Register.
> >
> > Signed-off-by: Pali Rohár <[email protected]>
> > Signed-off-by: Marek Behún <[email protected]>
> > Reviewed-by: Rob Herring <[email protected]>
> > ---
> > Changes in v2:
> > * Added support for PCIe 6.0 slot power limit encodings
> > * Round down slot power limit value
> > ---
> > drivers/pci/of.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++
> > drivers/pci/pci.h | 15 +++++++++++
> > 2 files changed, 79 insertions(+)
> >
> > diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> > index cb2e8351c2cc..549a404bd536 100644
> > --- a/drivers/pci/of.c
> > +++ b/drivers/pci/of.c
> > @@ -633,3 +633,67 @@ int of_pci_get_max_link_speed(struct device_node *node)
> > return max_link_speed;
> > }
> > EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);
> > +
> > +/**
> > + * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
> > + * property.
> > + *
> > + * @node: device tree node with the slot power limit information
> > + * @slot_power_limit_value: pointer where the value should be stored in PCIe
> > + * Slot Capabilities Register format
> > + * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
> > + * Slot Capabilities Register format
> > + *
> > + * Returns the slot power limit in milliwatts and if @slot_power_limit_value
> > + * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
> > + * scale in format used by PCIe Slot Capabilities Register.
> > + *
> > + * If the property is not found or is invalid, returns 0.
> > + */
> > +u32 of_pci_get_slot_power_limit(struct device_node *node,
> > + u8 *slot_power_limit_value,
> > + u8 *slot_power_limit_scale)
> > +{
> > + u32 slot_power_limit_mw;
> > + u8 value, scale;
> > +
> > + if (of_property_read_u32(node, "slot-power-limit-milliwatt",
> > + &slot_power_limit_mw))
> > + slot_power_limit_mw = 0;
> > +
> > + /* Calculate Slot Power Limit Value and Slot Power Limit Scale */
> > + if (slot_power_limit_mw == 0) {
> > + value = 0x00;
> > + scale = 0;
> > + } else if (slot_power_limit_mw <= 255) {
> > + value = slot_power_limit_mw;
> > + scale = 3;
> > + } else if (slot_power_limit_mw <= 255*10) {
> > + value = slot_power_limit_mw / 10;
> > + scale = 2;
> > + } else if (slot_power_limit_mw <= 255*100) {
> > + value = slot_power_limit_mw / 100;
> > + scale = 1;
> > + } else if (slot_power_limit_mw <= 239*1000) {
> > + value = slot_power_limit_mw / 1000;
> > + scale = 0;
> > + } else if (slot_power_limit_mw <= 250*1000) {
> > + value = 0xF0;
> > + scale = 0;
> > + } else if (slot_power_limit_mw <= 600*1000) {
> > + value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25;
> > + scale = 0;
> > + } else {
> > + value = 0xFF;
> > + scale = 0;
>
> The purpose of this function is to return values that can be
> programmed into the Slot Capabilities register. The 0xFF Slot Power
> Limit Value is reserved, and I don't think we should use it until the
> spec defines a meaning for it.
>
> If the DT tells us 800W is available, we'll put 0xFF in Slot Power
> Limit Value. If the spec eventually defines (0xFF, 0) to mean "1000W
> available", a device may try to consume all 1000W, which will not
> work.
>
> If slot_power_limit_mw > 600*1000, I think we should advertise 600W
> available (value 0xFE, scale 0) and return 600W (600*1000).
>
> Bjorn
Ok, I will send a v3 with this change.