linux-kernel - Re: [PATCH v2 2/2] media: i2c: add support for ov4689

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Date:   Mon, 19 Sep 2022 09:08:13 +0200
From:   Tommaso Merciai <tommaso.merciai@...rulasolutions.com>
To:     Mikhail Rudenko <mike.rudenko@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Shawn Tu <shawnx.tu@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Daniel Scally <djrscally@...il.com>,
        Christian Hemp <c.hemp@...tec.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Marek Vasut <marex@...x.de>, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] media: i2c: add support for ov4689

Hi Mikhail,

On Fri, Sep 16, 2022 at 04:44:31PM +0300, Mikhail Rudenko wrote:
> 
> On 2022-09-16 at 15:34 +02, Tommaso Merciai <tommaso.merciai@...rulasolutions.com> wrote:
> > Hi Mikhail,
> >
> > On Thu, Sep 15, 2022 at 11:50:23PM +0300, Mikhail Rudenko wrote:
> >>
> >> Hi Tommaso,
> >>
> >> On 2022-09-14 at 17:51 +02, Tommaso Merciai <tommaso.merciai@...rulasolutions.com> wrote:
> >> > Hi Mikhail,
> >> > I do a first round on reviewing your driver :)
> >> >
> >> > On Sun, Sep 11, 2022 at 11:01:35PM +0300, Mikhail Rudenko wrote:
> 
> <snip>
> 
> >> >> +
> >> >> +	ov4689->xvclk = devm_clk_get(dev, "xvclk");
> >> >> +	if (IS_ERR(ov4689->xvclk)) {
> >> >> +		dev_err(dev, "Failed to get xvclk\n");
> >> >> +		return -EINVAL;
> >> >> +	}
> >> >
> >> > ^ I think is better to use devm_clk_get_optional instead of clck_get.
> >> > clck_get can fail in CPU's that use ACPI
> >> >
> >> >> +
> >> >> +	ret = clk_set_rate(ov4689->xvclk, OV4689_XVCLK_FREQ);
> >> >> +	if (ret < 0) {
> >> >> +		dev_err(dev, "Failed to set xvclk rate (24MHz)\n");
> >> >> +		return ret;
> >> >> +	}
> >> >> +	if (clk_get_rate(ov4689->xvclk) != OV4689_XVCLK_FREQ)
> >> >> +		dev_warn(dev, "xvclk mismatched, modes are based on 24MHz\n");
> >> >
> >> >
> >> > What do you think about?
> >> > Thanks.
> >>
> >> Unfortunately, I have no experience with ACPI-based devices. :(
> >>
> >> Do you mean that in the case of an ACPI device and devm_clk_get_optional
> >> returning NULL we should assume that the clock is already enabled and
> >> will stay enabled during sensor operation? How should we distinguish it
> >> from the case of an OF-based system and clock just missing from device
> >> tree?
> >
> > Not exaclty :)
> >
> > I copy comment from [1]
> >
> > if you use ov5693->xvclk to identify the ACPI vs OF use case shouldn't
> > you use the get_optionl() version ? Otherwise in the ACPI case you will have
> > -ENOENT if there's not 'xvclk' property and bail out.
> >
> > Unless my understanding is wrong on ACPI we have "clock-frequency" and
> > on OF "xvclk" with an "assigned-clock-rates",
> >
> > [1] https://patchwork.linuxtv.org/project/linux-media/patch/20220627150453.220292-5-tommaso.merciai@amarulasolutions.com/
> >
> > Let me know if you need more details.
> 
> Thanks for the pointer! I'll try to implement something along the lines
> of your ov5693 series.
> 
> But I'm not sure that will be enough to support ACPI systems
> correctly. What about lanes number and link frequency checks? Should
> they be made conditional on CONFIG_OF? Anything else I don't know?

In my opinion, lanes number and link frequency checks are ok :)
We don't need conditional CONFIG_OF.

fwnode* function support both ACPI and dts.

Thanks,
Tommaso

> 
> >
> > Regards,
> > Tommaso
> >
> --
> Best regards,
> Mikhail Rudenko

-- 
Tommaso Merciai
Embedded Linux Engineer
tommaso.merciai@...rulasolutions.com
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