linux-kernel - Re: [PATCH v5 2/7] drm/ingenic: Add support for JZ4780 and HDMI output

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Message-Id: <0HO92R.RF221XL59J3I1@crapouillou.net>
Date:   Mon, 08 Nov 2021 18:53:24 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Harry Wentland <harry.wentland@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Paul Boddie <paul@...die.org.uk>,
        OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS 
        <devicetree@...r.kernel.org>,
        linux-mips <linux-mips@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, Jonas Karlman <jonas@...boo.se>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 2/7] drm/ingenic: Add support for JZ4780 and HDMI
 output

Hi Nikolaus,

Le lun., nov. 8 2021 at 19:33:48 +0100, H. Nikolaus Schaller 
<hns@...delico.com> a écrit :
> Hi Paul,
> 
>>  Am 08.11.2021 um 18:49 schrieb Paul Cercueil <paul@...pouillou.net>:
>> 
>>>>  Variant 4: the variant #2 without the changes to the DTSI files.
>>>  Hm. If there is no cache and we can safely remove tight boundary 
>>> checking (by JZ_REG_LCD_SIZE1) for jz4725/40/70 (by not fixing 
>>> DTSI) why do we still need the max_register calculation from DTSI 
>>> specifically for jz4780 and at all?
>> 
>>  It's better to have the .max_register actually set to the proper 
>> value. Then reading the registers from debugfs 
>> (/sys/kernel/debug/regmap/) will print the actual list of registers 
>> without bogus values. If .max_register is set too high, it will end 
>> up reading outside the registers area.
> 
> Ok, that is a good reason to convince me.
> 
>>  On Ingenic SoCs such reads just return 0, but on some other SoCs it 
>> can lock up the system.
> 
> Yes, I know some of these...
> 
>>  So the best way forward is to have .max_register computed from the 
>> register area's size, and fix the DTSI with the proper sizes. Since 
>> your JZ4780 code needs to update .max_register anyway it's a good 
>> moment to add this patch, and the DTSI files can be fixed later (by 
>> me or whoever is up to the task).
> 
> Well, it would already be part of my Variant #2 (untested). So I 
> could simply split it up further and you can test the pure dtsi 
> changes and apply them later or modify if that makes problems. Saves 
> you a little work. BTW: the jz4740 seems to have even less registers 
> (last register seems to be LCDCMD1 @ 0x1305005C).

Sure, if you want. Send the DTSI patch(es) separate from this patchset 
then.

>> 
>>  Fixing the DTS is not a problem in any way, btw. We just need to 
>> ensure that the drivers still work with old DTB files, which will be 
>> the case here.
> 
> Yes, that is right since the new values are smaller than the 
> originals.
> 
> Ok, then let's do it that way.

Great. Waiting for your v6 then.

Cheers,
-Paul