linux-kernel - Re: [PATCH 2/2] drm: lcdif: Add i.MX93 LCDIF support

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Message-ID: <13189854.uLZWGnKmhe@steina-w>
Date:   Tue, 24 Jan 2023 12:15:24 +0100
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Liu Ying <victor.liu@....com>
Cc:     Marek Vasut <marex@...x.de>, s.hauer@...gutronix.de,
        robh+dt@...nel.org, linux-imx@....com,
        krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 2/2] drm: lcdif: Add i.MX93 LCDIF support

Hi,

Am Dienstag, 24. Januar 2023, 08:59:39 CET schrieb Liu Ying:
> On Mon, 2023-01-23 at 16:57 +0100, Marek Vasut wrote:
> > On 1/23/23 08:23, Liu Ying wrote:
> > > The LCDIF embedded in i.MX93 SoC is essentially the same to those
> > > in i.MX8mp SoC.  However, i.MX93 LCDIF may connect with MIPI DSI
> > > controller through LCDIF cross line pattern(controlled by mediamix
> > > blk-ctrl) or connect with LVDS display bridge(LDB) directly or a
> > > parallel display(also through mediamix blk-ctrl), so add multiple
> > > encoders(with DRM_MODE_ENCODER_NONE encoder type) support in the
> > > LCDIF DRM driver and find a bridge to attach the relevant encoder's
> > > chain when needed.  While at it, derive lcdif_crtc_state structure
> > > from drm_crtc_state structure to introduce bus_format and bus_flags
> > > states so that the next downstream bridges may use consistent bus
> > > format and bus flags.
> > 
> > Would it be possible to split this patch into preparatory clean up
> > and
> > i.MX93 addition ? It seems like the patch is doing two things
> > according
> > to the commit message.
> 
> IMHO, all the patch does is for i.MX93 addition, not for clean up.
> Note that the single LCDIF embedded in i.MX93 SoC may connect with MIPI
> DSI/LVDS/parallel related bridges to drive triple displays
> _simultaneously_ in theory, while the three LCDIF instances embedded in
> i.MX8mp SoC connect with MIPI DSI/LVDS/HDMI displays respectively(one
> LCDIF maps to one display).  The multiple encoders addition and the new
> checks for consistent bus format and bus flags are only for i.MX93
> LCDIF, not for i.MX8mp LCDIF.  Also, I think the multiple encoders
> addition and the new checks should be done together - if the new checks
> come first, then the new checks do not make sense(no multiple displays
> driven by LCDIF); 

You are right on this one, but on the other hand there are lot of preparing 
patches already. Even if it is useless by itself, having the bus format & flag 
checks in a separate patch, it is easier to review, IMHO.

> if the new checks come later, then it would be a bug
> to allow inconsistent bus format and bus flags across the next
> downstream bridges when only adding multiple encoders support(also, I
> don't know which encoder's bridge should determine the LCDIF output bus
> format and bus flags, since the three encoders come together with the
> three next bridges).

Agreed, this order is a no-go.

Best regards,
Alexander

> Regards,
> Liu Ying