Re: [PATCH] drm/stm: Fix bus_flags handling

From: Marek Vasut <marex@denx.de>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: Alexandre Torgue <alexandre.torgue@st.com>,
	Antonio Borneo <antonio.borneo@st.com>,
	Philippe Cornu <philippe.cornu@st.com>,
	dri-devel@lists.freedesktop.org,
	Yannick Fertre <yannick.fertre@st.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Vincent Abriou <vincent.abriou@st.com>,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	Benjamin Gaignard <benjamin.gaignard@st.com>
Subject: Re: [PATCH] drm/stm: Fix bus_flags handling
Date: Tue, 20 Oct 2020 00:13:38 +0200	[thread overview]
Message-ID: <643e1594-99aa-cd2a-fa6f-836d60e57cab@denx.de> (raw)
In-Reply-To: <20201016174455.GB1333109@ravnborg.org>

On 10/16/20 7:44 PM, Sam Ravnborg wrote:
> Hi Marek.

Hi,

> On Sat, Oct 03, 2020 at 01:07:26AM +0200, Marek Vasut wrote:
>> The drm_display_mode_to_videomode() does not populate DISPLAY_FLAGS_DE_LOW
>> or DISPLAY_FLAGS_PIXDATA_NEGEDGE flags in struct videomode.
> 
> So after reading this paragrahp I assumed this patch would fix this, alas
> there is no changes to drm_modes.c.
> Rather than introducing hacks could we try to fix the root cause here?

Nope, this is a driver fix, hence the drm/stm tags.

> Root cause - as you point out is that there is missing some flags in
> the conversion.
> Another point is that the stm driver could drop the use of
> drm_display_mode_to_videomode() - all the information is available in drm_display_mode
> and using drm_display_mode_to_videomode() does not help much.

I kinda already have such a patch in the tree to remove this, but I want
to have a patch which fixes the problem described here and can be easily
backported to stable too.

> If the point is to have easier access to hsync and friendns maybe we
> should have a few helpers operating direct on display_mode and not this
> conversion to video_mode which is something that belongs to fbdev and
> should IMO not be used inside a drm driver.

Yep, that is for another patch though, because if that one breaks
something, I want to be able to bisect it.

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