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

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Date:	Tue, 05 Feb 2013 17:42:01 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Sean Paul <seanpaul@...omium.org>
CC:	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	dri-devel@...ts.freedesktop.org,
	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	"kgene.kim" <kgene.kim@...sung.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	InKi Dae <inki.dae@...sung.com>,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Olof Johansson <olofj@...omium.org>,
	RAHUL SHARMA <rahul.sharma@...sung.com>
Subject: Re: [PATCH v3 1/3] drm/exynos: Get HDMI version from device tree

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.

>>> @@ -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;
>>
>> 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.
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