linux-kernel - Re: [PATCH v4 04/15] drm/edid: Use new encoded panel id style for quirks matching

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Date:   Tue, 14 Sep 2021 21:59:23 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "open list\:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linus W <linus.walleij@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Steev Klimaszewski <steev@...i.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 04/15] drm/edid: Use new encoded panel id style for quirks matching

On Tue, 14 Sep 2021, Doug Anderson <dianders@...omium.org> wrote:
> Hi,
>
> On Tue, Sep 14, 2021 at 11:16 AM Jani Nikula
> <jani.nikula@...ux.intel.com> wrote:
>>
>> On Thu, 09 Sep 2021, Douglas Anderson <dianders@...omium.org> wrote:
>> > In the patch ("drm/edid: Allow the querying/working with the panel ID
>> > from the EDID") we introduced a different way of working with the
>> > panel ID stored in the EDID. Let's use this new way for the quirks
>> > code.
>> >
>> > Advantages of the new style:
>> > * Smaller data structure size. Saves 4 bytes per panel.
>> > * Iterate through quirks structure with just "==" instead of strncmp()
>> > * In-kernel storage is more similar to what's stored in the EDID
>> >   itself making it easier to grok that they are referring to the same
>> >   value.
>> >
>> > The quirk table itself is arguably a bit less readable in the new
>> > style but not a ton less and it feels like the above advantages make
>> > up for it.
>>
>> I suppose you could pass vendor as a string to EDID_QUIRK() to retain
>> better readability?
>
> I would love to, but I couldn't figure out how to do this and have it
> compile! Notably I need the compiler to be able to do math at compile
> time to compute the final u32 to store in the init data. I don't think
> the compiler can dereference strings (even constant strings) and do
> math on the result at compile time.

Ah, right.

>
> I _think_ you could make it work with four-character codes (only
> specifying 3 characters), AKA single-quoting something like 'AUO' but
> I think four-character codes are not dealt with in a standard enough
> way between compilers so they're not allowed in Linux.
>
> If you like it better, I could do something like this:
>
> #define ACR_CODE 'A', 'C', 'R'
> #define AUO_CODE 'A', 'U', 'O'
> ...
> ...
>
> ...then I could refer to the #defines...

Nah.

>
>
>> Just bikeshedding, really. ;)
>
> I'll take this comment (without any formal tags) as:
>
> * You've seen this patch (and the previous ones) and wouldn't object
> to it merging.
>
> * You're not planning on any deeper review / testing, so I shouldn't
> wait for more stuff from you before merging. Please yell if this is
> not the case. I'm happy to wait but I don't want to wait if no further
> review is planned.

I have now reviewed the ones where my review is relevant, and certainly
don't expect me to comment on the rest. ;)

BR,
Jani.

>
>
> In general I'm still planning to give this series at least another
> week for comments before merging. ${SUBJECT} patch also is the only
> one lacking any type of Review / Ack tags so I'll see if I can find
> someone to give it something before merging, too.
>
>
> -Doug

-- 
Jani Nikula, Intel Open Source Graphics Center