linux-kernel - Re: [PATCH 0/2] drm: add SimpleDRM driver

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Message-ID: <a6e7eb99-3ee1-1398-1660-cb6df1fe8f2c@redhat.com>
Date:	Fri, 5 Aug 2016 09:18:47 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Luc Verhaegen <libv@...net.be>,
	Noralf Trønnes <noralf@...nnes.org>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] drm: add SimpleDRM driver

Hi,

On 04-08-16 20:12, Luc Verhaegen wrote:
> On Thu, Aug 04, 2016 at 06:58:55PM +0200, Noralf Trønnes wrote:
>>
>> I didn't read the binding document[1], which I should have done.
>> If simpledrm claims to be compatible with simple-framebuffer I assume it
>> should support the entire binding doc which includes clocks, regulators
>> and having the node under /chosen.
>> I will lift the necessary code from simplefb.c and put it in the next
>> version.
>
> Smashing, repeat of a massive pain avoided, thanks :)
>
>> The binding doc also mentions an optional display phandle property, but I
>> can't find any reference to this in simplefb.c.

Ah yes, the display phandle, so the idea behind this is that the
simplefb node would have a display phandle pointing to a node
describing the "primary" node describing the actual display-pipe hardware.

The primary language is there because a display pipeline typically
consists of multiple blocks and thus has multiple nodes describing it.

This way the hardware driver would be able to figure out which simplefb
to disable if there is more then 1.

In practice the remove_conflicting_framebuffers kernel API is used for this and
that takes a framebuffer address, so that bit of the bindings is essentially
unused. Either way that bit is only relevant to the actual display hardware driver
(so that it can disable sumplefb when it takes over the display) and for
simpledrm you can simply ignore it.

Regards,

Hans

p.s.

Noralf, I recognize your name from the ft6236 touchscreen driver, I've mailed
you about this in the past because it is a duplicate driver, the edt-ft5x06
driver already speaks the same protocol. I see now that I made a copy and paste
error in your email address, so you never got my mails on this. I'll resend
my latest mail (a kernel patch removing the duplicate driver!) with a fixed
email address.