Date:	Wed, 06 Feb 2013 10:48:21 +0900
From:	Joonyoung Shim <jy0922.shim@...sung.com>
To:	Sean Paul <seanpaul@...omium.org>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	"kgene.kim" <kgene.kim@...sung.com>,
	devicetree-discuss@...ts.ozlabs.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org,
	Tomasz Figa <tomasz.figa@...il.com>,
	linux-samsung-soc@...r.kernel.org,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Olof Johansson <olofj@...omium.org>,
	linux-arm-kernel@...ts.infradead.org,
	RAHUL SHARMA <rahul.sharma@...sung.com>
Subject: Re: [PATCH v3 1/3] drm/exynos: Get HDMI version from device tree

On 02/06/2013 09:56 AM, Sean Paul wrote:
> On Tue, Feb 5, 2013 at 4:42 PM, Stephen Warren <swarren@...dotorg.org> wrote:
>> On 02/05/2013 05:37 PM, Sean Paul wrote:
>>> On Tue, Feb 5, 2013 at 4:22 PM, Stephen Warren <swarren@...dotorg.org> 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
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>

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