linux-kernel - Re: [PATCH v1 0/4] Add bus format negotiation support for Cadence MHDP8546 driver

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Date:   Mon, 16 Nov 2020 16:14:07 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Yuti Amonkar <yamonkar@...ence.com>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <maxime@...no.tech>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <mark.rutland@....com>, <a.hajda@...sung.com>,
        <narmstrong@...libre.com>, <Laurent.pinchart@...asonboard.com>,
        <jonas@...boo.se>, <jernej.skrabec@...l.net>
CC:     <nsekhar@...com>, <jsarha@...com>, <nikhil.nd@...com>,
        <mparab@...ence.com>, <sjakhade@...ence.com>
Subject: Re: [PATCH v1 0/4] Add bus format negotiation support for Cadence
 MHDP8546 driver

Hi,

On 13/11/2020 11:46, Yuti Amonkar wrote:
> This patch series add bus format negotiation support for Cadence MHDP8546 bridge
> driver.
> 
> The patch series has four patches in the below sequence:
> 1. drm: bridge: cdns-mhdp8546: Add output bus format negotiation
> Add minimal output bus format negotiation support.
> 2. drm: bridge: cdns-mhdp8546: Modify atomic_get_input_bus_format bridge function.
> Get the input format based on output format supported.
> 3. drm: bridge: cdns-mhdp8546: Remove setting of bus format using connector info
> Remove the bus format configuration using connector info structure.
> 4. drm: bridge: cdns-mhdp8546: Retrieve the pixel format and bpc based on bus format
> Get the pixel format and bpc based on negotiated output bus format.
> 
> This patch series is dependent on tidss series [1] for the new connector model support.
> 
> [1]
> https://patchwork.kernel.org/project/dri-devel/cover/20201109170601.21557-1-nikhil.nd@ti.com/ 

Can you explain how this works?

Afaics, what we should be doing is:

- We don't have proper bus formats for DP output, so we need to use MEDIA_BUS_FMT_FIXED as the
output format. This is what you do in the first patch. (But is that patch even needed, if
MEDIA_BUS_FMT_FIXED is the default anyway)

- In cdns_mhdp_get_input_bus_fmts, the function should exit if the given output format is not
MEDIA_BUS_FMT_FIXED.

- In cdns_mhdp_get_input_bus_fmts, the driver should return all the RGB bus formats, if MHDP is able
to upscale/downscale RGB (e.g. RGB 8-bpc to RGB 12-bpc).

- If the monitor supports YUV modes according to the display_info, cdns_mhdp_get_input_bus_fmts can
also return those.

- Then later, in atomic_check and commit, mhdp driver has the negotiated bus format, which it should
use to program the registers.

 Tomi

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