[PATCH 3/8] staging: media: imx: Add more compatible strings

[Laurent Pinchart]

Hi Jacopo,

On Tue, Feb 15, 2022 at 09:36:31AM +0100, Jacopo Mondi wrote:
> On Mon, Feb 14, 2022 at 09:15:07PM +0200, Laurent Pinchart wrote:
> > On Mon, Feb 14, 2022 at 07:43:13PM +0100, Jacopo Mondi wrote:
> > > The imx7-media-csi driver controls the CSI (CMOS Sensor Interface)
> > > peripheral available on several SoC of different generations.
> > >
> > > The current situation when it comes to compatible strings is rather
> > > confused:
> > > - Bindings document imx6ul, imx7 and imx8mm
> > > - Driver supports imx6ul, imx7 and imx8mq
> > > - The IMX8MM and IMX8MQ DTS use the correct compatible strings with a
> > >   fallback to the generic "imx7-csi" identifier:
> > >   arch/arm64/boot/dts/freescale/imx8mq.dtsi: compatible = "fsl,imx8mq-csi",
> > >   arch/arm64/boot/dts/freescale/imx8mm.dtsi: compatible = "fsl,imx8mm-csi",
> > >
> > > Tidy-up the situation by adding the IMX8MQ compatible string to the
> > > bindings documentation andathe IMX8MM identifier to the driver, to allow
> > > to distinguish the SoC the CSI peripheral is integrated on in the
> > > following patches.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > > ---
> > >  Documentation/devicetree/bindings/media/nxp,imx7-csi.yaml | 1 +
> > >  drivers/staging/media/imx/imx7-media-csi.c                | 2 ++
> >
> > I think Rob would prefer this being split in two patches, and I think it
> > would make sense, as you're fixing two separate issues.
> >
> > >  2 files changed, 3 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/media/nxp,imx7-csi.yaml b/Documentation/devicetree/bindings/media/nxp,imx7-csi.yaml
> > > index 4f7b78265336..0f1505d85111 100644
> > > --- a/Documentation/devicetree/bindings/media/nxp,imx7-csi.yaml
> > > +++ b/Documentation/devicetree/bindings/media/nxp,imx7-csi.yaml
> > > @@ -21,6 +21,7 @@ properties:
> > >            - fsl,imx7-csi
> > >            - fsl,imx6ul-csi
> > >        - items:
> > > +          - const: fsl,imx8mq-csi
> > >            - const: fsl,imx8mm-csi
> > >            - const: fsl,imx7-csi
> >
> > I don't think you intended to require the following:
> >
> > 	compatible = "fsl,imx8mq-csi", "fsl,imx8mm-csi", "fsl,imx7-csi";
> 
> No, I kind of superficially added the mq version where the mm was
> already and went on :)
> 
> Care to explain why currently we have two const for the "8mm" and the
> "imx7" versions ?

Because the imx8mm version was considered compatible with the imx7, so

       - items:
           - const: fsl,imx8mm-csi
           - const: fsl,imx7-csi

will validate

	compatible = "fsl,imx8mm-csi", "fsl,imx7-csi";

The first imx8mm compatible string is ignored by the driver, but
documented to support future drivers changes that would require
differentiating between the two versions.

> > You probably want
> >
> >  properties:
> >    compatible:
> >      oneOf:
> >        - enum:
> > +          - fsl,imx8mq-csi
> >            - fsl,imx7-csi
> >            - fsl,imx6ul-csi
> >        - items:
> >            - const: fsl,imx8mm-csi
> >            - const: fsl,imx7-csi
> >
> > instead.
> 
> I'm not aware of how how many revisions of the imx7 and imx6 versions
> exists, nor how they differ, but the existing distinction feels a bit
> weird.
> 
> The const items should be the compatible fallbacks, should them be
> generic, why is 8mm among them ? Shouldn't we specify the precise SoC
> version in the list of possible enum items only ?

No, the const items are not the compatible fallbacks. imx8mm isn't a
generic fallback. "items" requires *all* items to be present in order to
validate.

> Something like
> 
>       oneOf:
>         - enum:
>           - fsl,imx8mq-csi
>           - fsl,imx8mm-csi
>           - fsl,imx6ul-csi
>         - const:
>           - fsl,imx7-csi

That's not a valid schema.

> 
> In example I see:
> 
> arch/arm64/boot/dts/freescale/imx8mq.dtsi: compatible = "fsl,imx8mq-csi", "fsl,imx7-csi";
> 
> Where this should either be
>                                            compatible = "fsl,imx8mq-csi"
> or
>                                            compatible = "fsl,imx8mm-csi", "fsl,imx7-csi";
> 
> ?
> 
> > > diff --git a/drivers/staging/media/imx/imx7-media-csi.c b/drivers/staging/media/imx/imx7-media-csi.c
> > > index 32311fc0e2a4..59100e409709 100644
> > > --- a/drivers/staging/media/imx/imx7-media-csi.c
> > > +++ b/drivers/staging/media/imx/imx7-media-csi.c
> > > @@ -162,6 +162,7 @@
> > >  enum imx_csi_model {
> > >  	IMX7_CSI_IMX7 = 0,
> > >  	IMX7_CSI_IMX8MQ,
> > > +	IMX7_CSI_IMX8MM,
> > >  };
> > >
> > >  struct imx7_csi {
> > > @@ -1277,6 +1278,7 @@ static int imx7_csi_remove(struct platform_device *pdev)
> > >
> > >  static const struct of_device_id imx7_csi_of_match[] = {
> > >  	{ .compatible = "fsl,imx8mq-csi", .data = (void *)IMX7_CSI_IMX8MQ },
> > > +	{ .compatible = "fsl,imx8mm-csi", .data = (void *)IMX7_CSI_IMX8MM },
> >
> > This isn't needed, as the i.MX8MM CSI bridgge is considered fully
> > backward-compatible with the i.MX7 version. I'd introduce this change in
> > the patch where you start using IMX7_CSI_IMX8MM, and I would then add
> > the following to the DT binding:
> >
> >  properties:
> >    compatible:
> >      oneOf:
> >        - enum:
> >            - fsl,imx8mq-csi
> > +          - fsl,imx8mm-csi
> >            - fsl,imx7-csi
> >            - fsl,imx6ul-csi
> >        - items:
> >            - const: fsl,imx8mm-csi
> >            - const: fsl,imx7-csi
> >
> > to allow setting
> >
> > 	compatible = "fsl,imx8mm-csi";
> >
> > without the imx7 fallback if we consider the i.MX8MM version different.
> > If the driver can operate correctly on the i.MX8MM when using the i.MX7
> > fallback code paths (possibly minor issues that are not considered
> > fatal, such as missing features) then you could skip this binding
> > change.
> 
> Sorry, but shouldn't:
> 
>         compatible = "fsl,imx8mm-csi", fsl,imx7-csi"
> 
> allow me to match on imx8mm already, without the above change.
> 
> I think what I don't get is why imx8mm is a 'generic fallback' in
> first place.

See above.

> > >  	{ .compatible = "fsl,imx7-csi", .data = (void *)IMX7_CSI_IMX7 },
> > >  	{ .compatible = "fsl,imx6ul-csi", .data = (void *)IMX7_CSI_IMX7 },
> > >  	{ },

-- 
Regards,

Laurent Pinchart