linux-kernel - Re: [PATCH 2/2] media: qcom: camss: Restrict endpoint bus-type to D-PHY

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Message-Id: <D6AJ8KNRUHB7.1EC9O3WSCSNIP@fairphone.com>
Date: Fri, 13 Dec 2024 12:22:53 +0100
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Vladimir Zapolskiy" <vladimir.zapolskiy@...aro.org>, "Bryan O'Donoghue"
 <bryan.odonoghue@...aro.org>, "Robert Foss" <rfoss@...nel.org>, "Todor
 Tomov" <todor.too@...il.com>, "Mauro Carvalho Chehab" <mchehab@...nel.org>,
 "Rob Herring" <robh@...nel.org>, "Krzysztof Kozlowski"
 <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>, "Barnabas
 Czeman" <barnabas.czeman@...nlining.org>, "AngeloGioacchino Del Regno"
 <angelogioacchino.delregno@...ainline.org>, "Caleb Connolly"
 <caleb.connolly@...aro.org>, "David Heidelberg" <david@...t.cz>
Cc: <~postmarketos/upstreaming@...ts.sr.ht>, <phone-devel@...r.kernel.org>,
 <linux-arm-msm@...r.kernel.org>, <linux-media@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] media: qcom: camss: Restrict endpoint bus-type to
 D-PHY

On Fri Dec 13, 2024 at 12:02 PM CET, Vladimir Zapolskiy wrote:
> On 12/9/24 14:32, Bryan O'Donoghue wrote:
> > On 09/12/2024 12:01, Luca Weiss wrote:
> >> Currently the Qualcomm CAMSS driver only supports D-PHY while the
> >> hardware on most SoCs also supports C-PHY. Until this support is added,
> >> check for D-PHY to make it somewhat explicit that C-PHY won't work.
> >>
> >> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
> >> ---
> >>    drivers/media/platform/qcom/camss/camss.c | 9 +++++++++
> >>    1 file changed, 9 insertions(+)
> >>
> >> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> >> index 9fb31f4c18adee886cd0bcf84438a8f27635e07f..b99af35074cdf6fa794a0d2f0d54ecf12ac354d9 100644
> >> --- a/drivers/media/platform/qcom/camss/camss.c
> >> +++ b/drivers/media/platform/qcom/camss/camss.c
> >> @@ -1855,6 +1855,15 @@ static int camss_of_parse_endpoint_node(struct device *dev,
> >>    	if (ret)
> >>    		return ret;
> >>    
> >> +	/*
> >> +	 * Most SoCs support both D-PHY and C-PHY standards, but currently only
> >> +	 * D-PHY is supported in the driver.
> >> +	 */
> >> +	if (vep.bus_type != V4L2_MBUS_CSI2_DPHY) {
> >> +		dev_err(dev, "Unsupported bus type %d\n", vep.bus_type);
> >> +		return -EINVAL;
> >> +	}
> >> +
>
> Looks like it would break all old board dtbs, which is not just bad, but NAK.
>
> V4L2_MBUS_UNKNOWN shall be properly handled without the risk of regressions.

Please see drivers/media/v4l2-core/v4l2-fwnode.c around line 218.
The code there sets bus_type if it's UNKNOWN

    if (bus_type == V4L2_MBUS_UNKNOWN)
        vep->bus_type = V4L2_MBUS_CSI2_DPHY;

So setting "bus-type" in dt is not necessary, even if it makes things
more explicit from dt side. I don't think we'll ever get UNKNOWN here in
camss.

Regards
Luca


>
> >>    	csd->interface.csiphy_id = vep.base.port;
> >>    
> >>    	mipi_csi2 = &vep.bus.mipi_csi2;
> >>
> > 
> > Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> > 
>
> --
> Best wishes,
> Vladimir