by jacopo mondi

[permalink] [raw]

Subject: Re: [PATCH v3 11/19] media: i2c: rdacm21: Add dealy after OV490 reset

Hi Laurent, Kieran,

On Sat, Mar 20, 2021 at 05:52:18PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Fri, Mar 19, 2021 at 04:49:44PM +0000, Kieran Bingham wrote:
> > Hi Jacopo,
> >
> > s/dealy/delay/ in $SUBJECT
> >
> > On 19/03/2021 16:41, Jacopo Mondi wrote:
> > > Add a delay after the OV490 chip is put in reset state. The reset
> > > signal shall be held for at least 250 useconds.
> > >
> > > Signed-off-by: Jacopo Mondi <[email protected]>
> > > ---
> > > drivers/media/i2c/rdacm21.c | 6 +++++-
> > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> > > index babd14b21252..875bec9f7904 100644
> > > --- a/drivers/media/i2c/rdacm21.c
> > > +++ b/drivers/media/i2c/rdacm21.c
> > > @@ -448,7 +448,10 @@ static int rdacm21_init(struct v4l2_subdev *sd, unsigned int val)
> > > if (ret)
> > > return ret;
> > >
> > > - /* Enable GPIO1 and hold OV490 in reset during max9271 configuration. */
> > > + /*
> > > + * Enable GPIO1 and hold OV490 in reset during max9271 configuration.
> > > + * The reset signal has to be asserted for at least 250 useconds.
> > > + */
> > > ret = max9271_enable_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> > > if (ret)
> > > return ret;
> > > @@ -456,6 +459,7 @@ static int rdacm21_init(struct v4l2_subdev *sd, unsigned int val)
> > > ret = max9271_clear_gpios(&dev->serializer, MAX9271_GPIO1OUT);
> > > if (ret)
> > > return ret;
> > > + usleep_range(250, 500);
> >
> > Aha, for a second there I thought the comment meant it had to be
> > asserted for 250 uS before clearing it again. But it's 250 uS before
> > using the OV490.

No, it's 250usecond before releasing it. After the OV490 is released
from reset there's a 3-5 milliseconds sleep below.

> >
> > Perhaps possible to update the comment a little, but nothing that matters.
>
> The commit message and comment should match the code, especially given

They do if I'm not mistaken.

> that I'm not sure here which of the two is actually incorrect. I suspect
> the sleep is actually in the wrong location.
>
> > Reviewed-by: Kieran Bingham <[email protected]>
> >
> >
> > > ret = max9271_configure_gmsl_link(&dev->serializer);
> > > if (ret)
> > >
>
> --
> Regards,
>
> Laurent Pinchart

2021-03-26 11:38:39

by jacopo mondi

[permalink] [raw]

Subject: Re: [PATCH v3 05/19] media: v4l2-subdev: De-deprecate init() subdev op

Hi Sakari,

On Mon, Mar 22, 2021 at 01:51:44PM +0100, Jacopo Mondi wrote:
> Hi Sakari,
>
> On Sun, Mar 21, 2021 at 10:52:56PM +0200, Sakari Ailus wrote:
> > Hi Laurent and Jacopo,
> >
> > Thanks for cc'ing me.
> >
> > On Sat, Mar 20, 2021 at 05:42:12PM +0200, Laurent Pinchart wrote:
> > > Hi Jacopo,
> > >
> > > Thank you for the patch.
> > >
> > > CC'ing Sakari on v3 to get feedback.
> > >
> > > On Fri, Mar 19, 2021 at 05:41:34PM +0100, Jacopo Mondi wrote:
> > > > The init() subdev core operation is deemed to be deprecated for new
> > > > subdevice drivers. However it could prove useful for complex
> > > > architectures to defer operation that require access to the
> > > > communication bus if said bus is not available (or fully configured)
> > > > at the time when the subdevice probe() function is run.
> > > >
> > > > As an example, the GMSL architecture requires the GMSL configuration
> > > > link to be configured on the host side after the remote subdevice
> > > > has completed its probe function. After the configuration on the host
> > > > side has been performed, the subdevice registers can be accessed through
> > > > the communication bus.
> >
> > What does the remote device's probe do that needs to be done before bus
> > config on the host side?
>
> A few lines here below:
>
> In the GMSL use case the bus configuration requires the enablement of the
> noise immunity threshold on the remote side which ensures reliability
> of communications in electrically noisy environments. After the subdevice
> has enabled the threshold at the end of its probe() sequence the host
> side shall compensate it with an higher signal amplitude. Once this
> sequence has completed the bus can be accessed with noise protection
> enabled and all the operations that require a considerable number of
> transactions on the bus (such as the image sensor configuration
> sequence) are run in the subdevice init() operation implementation.
>
> >
> > Alternatively, could the remote init() work be done at the time streaming
> > is started?
>
> That would require programing the sensor, the embedded ISP at s_stream
> time which would take some time.

I'm afraid but from my testing also the chip identification is more
reliable if run in init(). As identifying chips is something that has
to happen at probe/initialization I fear it is not possible to move it
to s_stream time.

>
> I'll take this suggestion into account though and run some more tests.
>
> Thanks
> j
>
> >
> > > >
> > > > In particular:
> > > >
> > > > HOST REMOTE
> > > >
> > > > probe()
> > > > |
> > > > ---------------------> |
> > > > probe() {
> > > > bus config()
> > > > }
> > > > |<--------------------|
> > > > v4l2 async bound {
> > > > bus config()
> > > > call subdev init()
> > > > |-------------------->|
> > > > init() {
> > > > access register on the bus()
> > > > }
> > > > |<-------------------
> > > > }
> > > >
> > > > In the GMSL use case the bus configuration requires the enablement of the
> > > > noise immunity threshold on the remote side which ensures reliability
> > > > of communications in electrically noisy environments. After the subdevice
> > > > has enabled the threshold at the end of its probe() sequence the host
> > > > side shall compensate it with an higher signal amplitude. Once this
> > > > sequence has completed the bus can be accessed with noise protection
> > > > enabled and all the operations that require a considerable number of
> > > > transactions on the bus (such as the image sensor configuration
> > > > sequence) are run in the subdevice init() operation implementation.
> > > >
> > > > Signed-off-by: Jacopo Mondi <[email protected]>
> > > > ---
> > > > include/media/v4l2-subdev.h | 15 ++++++++++++---
> > > > 1 file changed, 12 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> > > > index d0e9a5bdb08b..3068d9940669 100644
> > > > --- a/include/media/v4l2-subdev.h
> > > > +++ b/include/media/v4l2-subdev.h
> > > > @@ -148,9 +148,18 @@ struct v4l2_subdev_io_pin_config {
> > > > * each pin being configured. This function could be called at times
> > > > * other than just subdevice initialization.
> > > > *
> > > > - * @init: initialize the sensor registers to some sort of reasonable default
> > > > - * values. Do not use for new drivers and should be removed in existing
> > > > - * drivers.
> > > > + * @init: initialize the subdevice registers to some sort of reasonable default
> > > > + * values. Do not use for new drivers (and should be removed in existing
> > > > + * ones) for regular architectures where the image sensor is connected to
> > > > + * the host receiver. For more complex architectures where the subdevice
> > > > + * initialization should be deferred to the completion of the probe
> > > > + * sequence of some intermediate component, or the communication bus
> > > > + * requires configurations on the host side that depend on the completion
> > > > + * of the probe sequence of the remote subdevices, the usage of this
> > > > + * operation could be considered to allow the devices along the pipeline to
> > > > + * probe and register in the media graph and to defer any operation that
> > > > + * require actual access to the communication bus to their init() function
> > > > + * implementation.
> > > > *
> > > > * @load_fw: load firmware.
> > > > *
> >
> > --
> > Kind regards,
> >
> > Sakari Ailus