linux-kernel - Re: [PATCH v2 2/2] drm/panel: Add driver for Novatek NT36523

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Date:   Wed, 8 Mar 2023 12:04:19 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Jianhua Lu <lujianhua000@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm/panel: Add driver for Novatek NT36523



On 8.03.2023 01:45, Jianhua Lu wrote:
> On Tue, Mar 07, 2023 at 11:34:55PM +0100, Linus Walleij wrote:
>> Hi Jianhua,
>>
>> thanks for your patch!
>>
>> It appears Konrad is working on a very similar driver, so I suggest merging
>> them into one Novatek NT36523 driver.
>>
>> Possibly we can fix this up first and then add Konrads Lenovo-panel with
>> a patch on top.
>>
>> On Mon, Feb 20, 2023 at 1:13 PM Jianhua Lu <lujianhua000@...il.com> wrote:
>>
>>> Add a driver for panels using the Novatek NT36523 display driver IC.
>>>
>>> Signed-off-by: Jianhua Lu <lujianhua000@...il.com>
>>
>> (...)
>>
>> I like how you abstract the panel with init commands in the panel info.
>>
>>> +enum dsi_cmd_type {
>>> +       INIT_DCS_CMD,
>>> +       DELAY_CMD,
>>> +};
>>> +
>>> +struct panel_init_cmd {
>>> +       enum dsi_cmd_type type;
>>> +       size_t len;
>>> +       const char *data;
>>> +};
>>> +
>>> +#define _INIT_DCS_CMD(...) { \
>>> +       .type = INIT_DCS_CMD, \
>>> +       .len = sizeof((char[]){__VA_ARGS__}), \
>>> +       .data = (char[]){__VA_ARGS__} }
>>> +
>>> +#define _INIT_DELAY_CMD(...) { \
>>> +       .type = DELAY_CMD,\
>>> +       .len = sizeof((char[]){__VA_ARGS__}), \
>>> +       .data = (char[]){__VA_ARGS__} }
>>
>> I have seen this type of reinvented wheels a few times now. Don't do this.
>>
>> Look into other recently merged drivers and look how they do it, for example
>> drivers/gpu/drm/panel/panel-himax-hx8394.c
>>
>> For example:
>>
>> - Use mipi_dsi_dcs_write_seq()
>>
>> - If the delay is just used at one point in the sequence, do not invent
>>   a command language like above for it, open code the delay instead
>>
>> - Try to decode as much magic as possible, if you look in Konrads
>>   driver you clearly see some standard MIPI commands, I bet you have
>>   some too.
>>
>> - Maybe use callbacks to send sequences instead of tables, like in
>>   the himax driver?
> Maybe I should create a wrapper of mipi_dsi_dcs_write_seq() for sync dual dsi mode.
Yes please, it'll come in useful.

Konrad
>>
>> Other than that it seems like something that could also handle the Lenovo
>> display, or the other way around, I don't know which driver is the best
>> starting point, but this one has the right Novatek name at least.
>>
>> Yours,
>> Linus Walleij