Re: [PATCH 07/12] arch/x86: Declare edid_info in <asm/screen_info.h>

From: Thomas Zimmermann <tzimmermann@suse.de>
To: Arnd Bergmann <arnd@arndb.de>, Helge Deller <deller@gmx.de>,
	Daniel Vetter <daniel@ffwll.ch>, Dave Airlie <airlied@gmail.com>
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	Kees Cook <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	Juerg Haefliger <juerg.haefliger@canonical.com>
Subject: Re: [PATCH 07/12] arch/x86: Declare edid_info in <asm/screen_info.h>
Date: Thu, 29 Jun 2023 15:01:13 +0200	[thread overview]
Message-ID: <d3de124c-6aa8-e930-e238-7bd6dd7929a6@suse.de> (raw)
In-Reply-To: <80e3a583-805e-4e8f-a67b-ebe2e4b9a7e5@app.fastmail.com>

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Hi

Am 29.06.23 um 14:35 schrieb Arnd Bergmann:
> On Thu, Jun 29, 2023, at 13:45, Thomas Zimmermann wrote:
>> The global variable edid_info contains the firmware's EDID information
>> as an extension to the regular screen_info on x86. Therefore move it to
>> <asm/screen_info.h>.
>>
>> Add the Kconfig token ARCH_HAS_EDID_INFO to guard against access on
>> architectures that don't provide edid_info. Select it on x86.
> 
> I'm not sure we need another symbol in addition to
> CONFIG_FIRMWARE_EDID. Since all the code behind that
> existing symbol is also x86 specific, would it be enough
> to just add either 'depends on X86' or 'depends on X86 ||
> COMPILE_TEST' there?

FIRMWARE_EDID is a user-selectable feature, while ARCH_HAS_EDID_INFO 
announces an architecture feature. They do different things.

Right now, ARCH_HAS_EDID_INFO only works on the old BIOS-based VESA 
systems. In the future, I want to add support for EDID data from EFI and 
OF as well. It would be stored in edid_info. I assume that the new 
symbol will become useful then.

Before this patchset, I originally wanted to make use of edid_info in 
the simpledrm graphics driver. But I found that the rsp code could use 
some work first. Maybe the patchset are already tailored towards the 
future changes.

Best regards
Thomas

> 
>        Arnd

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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