Hi Am 05.05.22 um 10:28 schrieb Javier Martinez Canillas:
Hello Thomas, On 5/5/22 10:05, Thomas Zimmermann wrote: [snip]In other words, in most cases (i.e: only fbcon bound to the fbdev) the driver's removal/ device unbind and the memory release will be at the same time.We're one the same page here, but it's still sort of a mystery to me why this works in practice. I'm specifically talking about pci_request_regions() in vmwgfx [1]. IIRC this would fail if simplefb still owns the framebuffer region. Lots of systems run Plymouth during boot and this should result in failures occasionally. Still, we never heard about anything.Yes, I think is because Plymouth IIUC waits for a /dev/dri/card? to be present and only uses a /dev/fb? as a fallback if a timeout expires.
Oh, right! The infamous plymouth timeout. 'sleep(30)' is the swiss-army knife of concurrent programming. ;)
But I'm not blaming anyone. There are situations where nothing else helps. Plymouth really can't do anything else here. We've received reports for gfx-handover bugs when the timeout expired and plymouth uses the fbdev. The system got stuck then because of fbdev IIRC.
Best regards Thomas
At least in Fedora (even before the efifb -> simpledrm change) it will use KMS/DRM since the DRM kernel module for the graphics device in the machine would be in the intird. So efifb was only used for fbcon and plymouth would only use DRM/KMS and not its fbdev backend. This seems to be sort of a corner case when you have {efi,simple}fb in the early boot but the real DRM module only in the rootfs after the initrd has done a pivot_root(2).Of course, it's always been broken (even long before real fbdev hotunplugging). Switching to simpledrm resolves the problem.Indeed. My opinion after dealing with these fbdev problems is that we shouldn't try to fix all possible corner cases and just try to get rid of fbdev as soon as possible. -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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