Re: [RFC PATCH] drm/panel: simple: panel-dpi: use bus-format to set bpc and bus_format

From: Marek Vasut <marex@denx.de>
To: Maxime Ripard <maxime@cerno.tech>,
	Max Krummenacher <max.oss.09@gmail.com>
Cc: dri-devel@lists.freedesktop.org,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Fabio Estevam <festevam@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	DenysDrozdov <denys.drozdov@toradex.com>,
	David Airlie <airlied@linux.ie>,
	Christoph Niedermaier <cniedermaier@dh-electronics.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Sam Ravnborg <sam@ravnborg.org>, Shawn Guo <shawnguo@kernel.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	NXP Linux Team <linux-imx@nxp.com>,
	Max Krummenacher <max.krummenacher@toradex.com>
Subject: Re: [RFC PATCH] drm/panel: simple: panel-dpi: use bus-format to set bpc and bus_format
Date: Wed, 2 Mar 2022 17:22:07 +0100	[thread overview]
Message-ID: <9c9a10ca-e6a1-c310-c0a5-37d4fed6efd6@denx.de> (raw)
In-Reply-To: <20220302142142.zroy464l5etide2g@houat>

On 3/2/22 15:21, Maxime Ripard wrote:
> Hi,

Hi,

> Please try to avoid top posting
> 
> On Wed, Feb 23, 2022 at 04:25:19PM +0100, Max Krummenacher wrote:
>> The goal here is to set the element bus_format in the struct
>> panel_desc. This is an enum with the possible values defined in
>> include/uapi/linux/media-bus-format.h.
>>
>> The enum values are not constructed in a way that you could calculate
>> the value from color channel width/shift/mapping/whatever. You rather
>> would have to check if the combination of color channel
>> width/shift/mapping/whatever maps to an existing value and otherwise
>> EINVAL out.
>>
>> I don't see the value in having yet another way of how this
>> information can be specified and then having to write a more
>> complicated parser which maps the dt data to bus_format.
> 
> Generally speaking, sending an RFC without explicitly stating what you
> want a comment on isn't very efficient.

Isn't that what RFC stands for -- Request For Comment ?

> That being said, what I (and I can only assume Marek) don't like is the
> string encoding. Especially when the similar bus-type property uses a
> integer with the various available bus options we have.

Right, the string encoding isn't good.

> Having an integer, with a set of defines that you would map to the
> proper MEDIA_BUS_* would be more efficient and more elegant.
> 
> That being said, the first question that needs to be answered is why
> does this have to be in the DT in the first place?

Because panel-simple panel-dpi , you may need to specify the bus format 
between the last bridge and the panel .

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