Hi Am 29.06.23 um 15:21 schrieb Arnd Bergmann:
On Thu, Jun 29, 2023, at 15:01, Thomas Zimmermann wrote: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.I still have trouble seeing the difference.
The idea here is that ARCH_HAS_ signals the architecture's support for the feature. Drivers set 'depends on' in their Kconfig.
Another Kconfig token, VIDEO_SCREEN_INFO or FIRMWARE_EDID, would then actually enable the feature. Drivers select VIDEO_SCREEN_INFO or FIRMWARE_EDID and the architectures contains code like
#ifdef VIDEO_SCREEN_INFO
struct screen_info screen_info = {
/* set values here */
}
#endif
This allows us to disable code that requires screen_info/edid_info, but
also disable screen_info/edid_info unless such code has been enabled in
the kernel config.
Some architectures currently mimic this by guarding screen_info with ifdef CONFIG_VT or similar. I'd like to make this more flexible. The cost of a few more internal Kconfig tokens seems negligible.
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.I don't see why an OF based system would have the same limitation as legacy BIOS with supporting only a single monitor, if we need to have a generic representation of EDID data in DT, that would probably be in a per device property anyway.
Sorry that was my mistake. OF has nothing to do with this.
I suppose you could use FIRMWARE_EDID on EFI or OF systems without the need for a global edid_info structure, but that would not share any code with the current fb_firmware_edid() function.
The current code is build on top of screen_info and edid_info. I'd preferably not replace that, if possible.
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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