On Tue, Apr 02, 2024 at 06:55:34PM +0300, Jani Nikula wrote:
The display param duplication deviates from the original param duplication in that it converts NULL params to to allocated empty strings. This works for the vbt_firmware parameter, but not for dmc_firmware_path, the user of which interprets NULL and the empty string as distinct values. Specifically, the empty dmc_firmware_path leads to DMC and PM being disabled.Just remove the NULL check and pass it to kstrdup(), which safely returns NULL for NULL input. Fixes: 8015bee0bfec ("drm/i915/display: Add framework to add parameters specific to display") Fixes: 0d82a0d6f556 ("drm/i915/display: move dmc_firmware_path to display params") Cc: Jouni Högander <[email protected]> Cc: Luca Coelho <[email protected]> Cc: <[email protected]> # v6.8+ Signed-off-by: Jani Nikula <[email protected]>
Reviewed-by: Lucas De Marchi <[email protected]> ... but what's the purpose of the duplication? How one is supposed to use the dmc_firmware with e.g. LNL + BMG? Setting it later via debugfs doesn´t change the behavior. AFAIR this was done to support multiple devices, but I don't think it achieves its purpose or I'm missing something. By leaving a param writable and not duplicate it at all, we are at least be allowed to: 1) disable autoprobe 2) load module 3) bind do LNL 4) set dmc_firmware param 5) bind to BMG Yeah, it's manual and not intuitive, but should only be used by developers with targeted debug. How would we do something like that with the current code? I know that for params via sysfs, it's impossible to get them back to NULL, so I think we should make sure NULL and empty is handled the same way. Getting it back to empty is hard enough but at least possible (see https://lore.kernel.org/igt-dev/[email protected]/), but I think this is not the case for debugfs. Lucas De Marchi
