linux-kernel - Re: [PATCH 4/5] drm/connector: Split out orientation quirk detection

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Date:   Wed, 12 Jun 2019 14:33:05 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "dbasehore ." <dbasehore@...omium.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH 4/5] drm/connector: Split out orientation quirk detection

Hi,

On 12-06-19 02:16, dbasehore . wrote:
> On Tue, Jun 11, 2019 at 1:54 AM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> Hi,
>>
>> On 11-06-19 10:08, Jani Nikula wrote:
>>> On Mon, 10 Jun 2019, Derek Basehore <dbasehore@...omium.org> wrote:
>>>> This removes the orientation quirk detection from the code to add
>>>> an orientation property to a panel. This is used only for legacy x86
>>>> systems, yet we'd like to start using this on devicetree systems where
>>>> quirk detection like this is not needed.
>>>
>>> Not needed, but no harm done either, right?
>>>
>>> I guess I'll defer judgement on this to Hans and Ville (Cc'd).
>>
>> Hmm, I'm not big fan of this change. It adds code duplication and as
>> other models with the same issue using a different driver or panel-type
>> show up we will get more code duplication.
>>
>> Also I'm not convinced that devicetree based platforms will not need
>> this. The whole devicetree as an ABI thing, which means that all
>> devicetree bindings need to be set in stone before things are merged
>> into the mainline, is done solely so that we can get vendors to ship
>> hardware with the dtb files included in the firmware.
> 
> We've posted fixes to the devicetree well after the initial merge into
> mainline before, so I don't see what you mean about the bindings being
> set in stone.

That was just me repeating the official party line about devicetree.

> I also don't really see the point. The devicetree is in
> the kernel. If there's some setting in the devicetree that we want to
> change, it's effectively the same to make the change in the devicetree
> versus some quirk setting. The only difference seems to be that making
> the change in the devicetree is cleaner.

I agree with you that devicetree in practice is easy to update after
shipping. But at least whenever I tried to get new bindings reviewed
I was always told that I was not allowed to count on that.

>> I'm 100% sure that there is e.g. ARM hardware out there which uses
>> non upright mounted LCD panels (I used to have a few Allwinner
>> tablets which did this). And given my experience with the quality
>> of firmware bundled tables like ACPI tables I'm quite sure that
>> if we ever move to firmware included dtb files that we will need
>> quirks for those too.
> 
> Is there a timeline to start using firmware bundled tables?

Nope, as I said "if we ever move to ...".

> Since the
> quirk code only uses DMI, it will need to be changed anyways for
> firmware bundled devicetree files anyways.
> 
> We could consolidate the duplicated code into another function that
> calls drm_get_panel_orientation_quirks too. The only reason it's like
> it is is because I initially only had the call to
> drm_get_panel_orientation_quirk once in the code.

Yes if you can add a new helper for the current callers, then
I'm fine with dropping the quirk handling from
drm_connector_init_panel_orientation_property()

Regards,

Hans