Re: [PATCH] drm/vmwgfx: Stop requesting the pci regions

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Hi

Am 19.01.22 um 16:12 schrieb Zack Rusin:
On Wed, 2022-01-19 at 15:00 +0100, Thomas Zimmermann wrote:
Hi Zack

Am 19.01.22 um 10:13 schrieb Thomas Zimmermann:
Hi

Am 19.01.22 um 03:15 schrieb Zack Rusin:
On Tue, 2022-01-18 at 20:00 +0100, Javier Martinez Canillas wrote:
Hello Zack,

On 1/17/22 19:03, Zack Rusin wrote:
From: Zack Rusin <zackr@xxxxxxxxxx>

When sysfb_simple is enabled loading vmwgfx fails because the
regions
are held by the platform. In that case
remove_conflicting*_framebuffers
only removes the simplefb but not the regions held by sysfb.


Indeed, that's an issue. I wonder if we should drop the
IORESOURCE_BUSY
flag from the memory resource added to the "simple-framebuffer"
device
?

I think this is one of those cases where it depends on what we plan
to
do after that. Sementically it makes sense to have it in there -
the
framebuffer memory is claimed by the "simple-framebuffer" and it's
busy, it's just that it creates issues for drivers after unloading.
I
think removing it, while making things easier for drivers, would be
confusing for people reading the code later, unless there's some
kind
of cleanup that would happen with it (e.g. removing IORESOURCE_BUSY
altogether and making the drm drivers properly request their
resources). At least by itself it doesn't seem to be much better
solution than having the drm drivers not call
pci_request_region[s],
which apart from hyperv and cirrus (iirc bochs does it for
resources
other than fb which wouldn't have been claimed by "simple-
framebuffer")
is already the case.

I do think we should do one of them to make the codebase coherent:
either remove IORESOURCE_BUSY from "simple-framebuffer" or remove
pci_request_region[s] from hyperv and cirrus.

I just discussed this a bit with Javier. It's a problem with the
simple-framebuffer code, rather then vmwgfx.

IMHO the best solution is to drop IORESOURCE_BUSY from sysfb and have
drivers register/release the range with _BUSY. That would signal the
memory belongs to the sysfb device but is not busy unless a driver
has
been bound. After simplefb released the range, it should be 'non-
busy'
again and available for vmwgfx. Simpledrm does a hot-unplug of the
sysfb
device, so the memory range gets released entirely. If you want, I'll
prepare some patches for this scenario.

Attached is a patch that implements this. Doing

   cat /proc/iomem
    ...
    e0000000-efffffff : 0000:00:02.0

      e0000000-e07e8fff : BOOTFB

        e0000000-e07e8fff : simplefb

    ...

shows the memory. 'BOOTFB' is the simple-framebuffer device and
'simplefb' is the driver. Only the latter uses _BUSY. Same for
and the memory canbe acquired by vmwgfx.

Zack, please test this patch. If it works, I'll send out the real
patchset.

Hmm, the patch looks good but it doesn't work. After boot: /proc/iomem
50000000-7fffffff : pcie@0x40000000
   78000000-7fffffff : 0000:00:0f.0
     78000000-782fffff : BOOTFB

and vmwgfx fails on pci_request_regions:

kernel: fb0: switching to vmwgfx from simple
kernel: Console: switching to colour dummy device 80x25
kernel: vmwgfx 0000:00:0f.0: BAR 2: can't reserve [mem 0x78000000-
0x7fffffff 64bit pref]
kernel: vmwgfx: probe of 0000:00:0f.0 failed with error -16

leaving the system without a fb driver.

OK, I suspect that it would work if you use simpledrm instead of simplefb. Could you try please? You'd have to build DRM and simpledrm into the kernel binary.

If that works, would you consider protecting pci_request_region() with
 #if not defined(CONFIG_FB_SIMPLE)
 #endif

with a FIXME comment?

simpledrm hot-unplugs the sysfb device entirely. Maybe simplefb can do the same. I'm not sure, but possibly.

Best regards
Thomas


z

--
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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