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

[Thomas Zimmermann]

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 at vmware.com>
>>>>>>
>>>>>> 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 at 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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