linux-kernel - Re: [PATCH v2 01/13] media: i2c: imx214: Fix link frequency

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Message-ID: <ZySa4gBDjJS7q-yI@kekkonen.localdomain>
Date: Fri, 1 Nov 2024 09:09:54 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Ricardo Ribalda Delgado <ribalda@...nel.org>
Cc: git@...tzsch.eu, Mauro Carvalho Chehab <mchehab@...nel.org>,
	~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v2 01/13] media: i2c: imx214: Fix link frequency

Hi Ricardo, André,

On Wed, Oct 30, 2024 at 12:25:25PM +0100, Ricardo Ribalda Delgado wrote:
> Hi Andre
> 
> On Mon, Oct 21, 2024 at 12:14 AM André Apitzsch via B4 Relay
> <devnull+git.apitzsch.eu@...nel.org> wrote:
> >
> > From: André Apitzsch <git@...tzsch.eu>
> >
> > The driver defines IMX214_DEFAULT_LINK_FREQ 480000000, and then
> > IMX214_DEFAULT_PIXEL_RATE ((IMX214_DEFAULT_LINK_FREQ * 8LL) / 10),
> > which works out as 384MPix/s. (The 8 is 4 lanes and DDR.)
> >
> > Parsing the PLL registers with the defined 24MHz input. We're in single
> > PLL mode, so MIPI frequency is directly linked to pixel rate.  VTCK ends
> > up being 1200MHz, and VTPXCK and OPPXCK both are 120MHz.  Section 5.3
> > "Frame rate calculation formula" says "Pixel rate
> > [pixels/s] = VTPXCK [MHz] * 4", so 120 * 4 = 480MPix/s, which basically
> > agrees with my number above.
> >
> > 3.1.4. MIPI global timing setting says "Output bitrate = OPPXCK * reg
> > 0x113[7:0]", so 120MHz * 10, or 1200Mbit/s. That would be a link
> > frequency of 600MHz due to DDR.
> > That also matches to 480MPix/s * 10bpp / 4 lanes / 2 for DDR.
> >
> I think your calculations are correct and the value should be 600M...
> but if we land this change, there will be boards that will stop
> working until they update their dts.
> Not sure if we allow that.
> 
> Can we move this change to the last one of the series and add something like:
> 
> diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
> index 2aca3d88a0a7..8b4ded4cb5ce 100644
> --- a/drivers/media/i2c/imx214.c
> +++ b/drivers/media/i2c/imx214.c
> @@ -1281,13 +1281,9 @@ static int imx214_parse_fwnode(struct device
> *dev, struct imx214 *imx214)
>                 if (bus_cfg.link_frequencies[i] == IMX214_DEFAULT_LINK_FREQ)
>                         break;
> 
> -       if (i == bus_cfg.nr_of_link_frequencies) {
> -               dev_err_probe(dev, -EINVAL,
> -                             "link-frequencies %d not supported,
> Please review your DT\n",
> +       if (i == bus_cfg.nr_of_link_frequencies)
> +               dev_warn(dev, "link-frequencies %d not supported,
> Please review your DT. Continuing anyway\n",
>                               IMX214_DEFAULT_LINK_FREQ);

I'd also add a check it's the frequency supported by the driver previously,
not any frequency. There will be problems if 480 MHz will be actually
supported in the future.

> -               ret = -EINVAL;
> -               goto done;
> -       }
> 
> 
> 
> > Signed-off-by: André Apitzsch <git@...tzsch.eu>
> > ---
> >  drivers/media/i2c/imx214.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
> > index 4962cfe7c83d62425aeccb46a400fa93146f14ea..5d411452d342fdb177619cd1c9fd9650d31089bb 100644
> > --- a/drivers/media/i2c/imx214.c
> > +++ b/drivers/media/i2c/imx214.c
> > @@ -24,7 +24,7 @@
> >  #define IMX214_MODE_STREAMING          0x01
> >
> >  #define IMX214_DEFAULT_CLK_FREQ        24000000
> > -#define IMX214_DEFAULT_LINK_FREQ 480000000
> > +#define IMX214_DEFAULT_LINK_FREQ 600000000
> >  #define IMX214_DEFAULT_PIXEL_RATE ((IMX214_DEFAULT_LINK_FREQ * 8LL) / 10)
> >  #define IMX214_FPS 30
> >  #define IMX214_MBUS_CODE MEDIA_BUS_FMT_SRGGB10_1X10
> >

-- 
Kind regards,

Sakari Ailus