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

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Date:	Tue, 5 Feb 2013 16:56:31 -0800
From:	Sean Paul <seanpaul@...omium.org>
To:	Stephen Warren <swarren@...dotorg.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 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;
>>>
>>> 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 */
        }
};

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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