Hi Jacopo,
Thank you for the patch.
On Mon, May 06, 2024 at 04:49:46PM +0200, Jacopo Mondi wrote:
> In order to start streaming, the serializer's SEREN bit has to
> be asserted and the video link enabled. In order for the video
> link to be enabled correctly a valid pixel clock has to be
> detected between the serializer and the connected image sensor.
>
> The pixel clock detection is performed by reading register 0x15 but the
> first attempt to read the register value sporadically fails resulting in
> a error in the stream start procedure.
>
> As the error is not fatal, and the pixel detection procedure will abort
> anyway after 10 msec if no valid pixel clock is detected, continue
> instead of failing immediately if the register read fails.
>
> Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx>
>
> ---
> When running 4 cameras at a time, the first register read on the first started
> camera fails pretty often. I here decided to ignore the error and go for another
> read attempt, but issuing a simple "i2c_smbus_read_reg()" (as we do in the wakup
> function) before the actual register read resolves the issue in the same way.
>
> I've not been able to find in the datasheet any mention of a "ping to wakeup"
> requirement before enabling the video channel, but this change make capturing
> from 4 RDACM20 camera pretty reliable.
I'm OK with that. In parallel, it would be nice to try and ask the
vendor (assuming they would still provide support for GMSL).
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> ---
>
> drivers/media/i2c/max9271.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/i2c/max9271.c b/drivers/media/i2c/max9271.c
> index ff86c8c4ea61..e339dff3986d 100644
> --- a/drivers/media/i2c/max9271.c
> +++ b/drivers/media/i2c/max9271.c
> @@ -66,8 +66,10 @@ static int max9271_pclk_detect(struct max9271_device *dev)
>
> for (i = 0; i < 100; i++) {
> ret = max9271_read(dev, 0x15);
> - if (ret < 0)
> - return ret;
> + if (ret < 0) {
> + usleep_range(50, 100);
> + continue;
> + }
>
> if (ret & MAX9271_PCLKDET)
> return 0;
--
Regards,
Laurent Pinchart
