Re: [PATCH v3 1/3] drm/exynos: Get HDMI version from device tree

[Joonyoung Shim]

On 02/06/2013 09:56 AM, Sean Paul wrote:
> On Tue, Feb 5, 2013 at 4:42 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> > On 02/05/2013 05:37 PM, Sean Paul wrote:
> > > On Tue, Feb 5, 2013 at 4:22 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> > > > n 02/05/2013 04:42 PM, Sean Paul wrote:
> > > > > Use the compatible string in the device tree to determine which
> > > > > registers/functions to use in the HDMI driver. Also changes the
> > > > > references from v13 to 4210 and v14 to 4212 to reflect the IP
> > > > > block version instead of the HDMI version.
> > > > > diff --git a/Documentation/devicetree/bindings/drm/exynos/hdmi.txt b/Documentation/devicetree/bindings/drm/exynos/hdmi.txt
> > > > Binding looks sane to me.
> > > >
> > > > > diff --git a/drivers/gpu/drm/exynos/exynos_hdmi.c b/drivers/gpu/drm/exynos/exynos_hdmi.c
> > > > >   #ifdef CONFIG_OF
> > > > >   static struct of_device_id hdmi_match_types[] = {
> > > > >        {
> > > > > -             .compatible = "samsung,exynos5-hdmi",
> > > > > -             .data   = (void *)HDMI_TYPE14,
> > > > > +             .compatible = "samsung,exynos4-hdmi",
> > > > >        }, {
> > > > >                /* end node */
> > > > >        }
> > > > Why not fill in all the "base" compatible values there (I think you need
> > > > this anyway so that DTs don't all have to be compatible with
> > > > samsung,exynos4-hdmi), with .data containing the HDMI_VER_EXYNOS*
> > > > values, then ...
> > > At the moment, all DTs have to be compatible with exynos4-hdmi since
> > > it provides the base for the current driver. The driver uses 4210 and
> > > 4212 to differentiate between different register addresses and
> > > features, but most things are just exynos4-hdmi compatible.
> > The DT nodes should include only the compatible values that the HW is
> > actually compatible with. If the HW isn't compatible with exynos4-hdmi,
> > that value shouldn't be in the compatible property, but instead whatever
> > the "base" value that the HW really is compatible with. The driver can
> > support multiple "base" compatible values from this table.
> All devices that use this driver are compatible, at some level, with
> exynos4-hdmi, so I think its usage is correct here.
>
> > > > > @@ -2218,17 +2217,18 @@ static int hdmi_probe(struct platform_device *pdev)
> > > > > +
> > > > > +     if (of_device_is_compatible(dev->of_node, "samsung,exynos4210-hdmi"))
> > > > > +             hdata->version |= HDMI_VER_EXYNOS4210;
> > > > > +     if (of_device_is_compatible(dev->of_node, "samsung,exynos4212-hdmi"))
> > > > > +             hdata->version |= HDMI_VER_EXYNOS4212;
> > > > > +     if (of_device_is_compatible(dev->of_node, "samsung,exynos5250-hdmi"))
> > > > > +             hdata->version |= HDMI_VER_EXYNOS5250;

But this way can make unnecessary combinations, e.g. exynos4210-hdmi + 
exynos5250-hdmi.

> > > > Instead of that, do roughly:
> > > >
> > > >      match = of_match_device(hdmi_match_types, &pdev->dev);
> > > >      if (match)
> > > >          hdata->version |= (int)match->data;
> > > >
> > > > That way, it's all table-based. Any future additions to
> > > > hdmi_match_types[] won't require another if statement to be added to
> > > > probe().
> > > I don't think it's that easy. of_match_device returns the first match
> > > from the device table, so I'd still need to iterate through the
> > > matches. I could still break this out into a table, but I don't think
> > > of_match_device is the right way to probe it.
> > You shouldn't have to iterate over multiple matches. of_match_device()
> > is supposed to return the match for the first entry in the compatible
> > property, then if there was no match, move on to looking at the next
> > entry in the compatible property, etc. In practice, I think it's still
> > not implemented quite correctly for this, but you can make it work by
> > putting the newest compatible value first in the match table.
> I think the only way that works is if you hardcode the compatible
> versions in the driver, like this:
>
> static struct of_device_id hdmi_match_types[] = {
>          {
>                  .compatible = "samsung,exynos5250-hdmi",
>                  .data = (void *)(HDMI_VER_EXYNOS5250 | HDMI_VER_EXYNOS4212);
>          }, {
>                  .compatible = "samsung,exynos4212-hdmi",
>                  .data = (void *)HDMI_VER_EXYNOS4212;
>          }, {
>                  .compatible = "samsung,exynos4210-hdmi",
>                  .data = (void *)HDMI_VER_EXYNOS4210;
>          }, {
>                  /* end node */
>          }
> };

I think this makes driver more clearly. We just see device tables and we 
can know device uses which version.

> In that case, it eliminates the benefit of using device tree to
> determine the compatible bits. I hope I'm just being thick and missing
> something.
>
> Sean
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