Re: [PATCH v2 07/11] video/aperture: Disable and unregister sysfb devices via aperture helpers

From: Thomas Zimmermann <tzimmermann@suse.de>
To: "Samuel Čavoj" <samuel@cavoj.net>
Cc: javierm@redhat.com, deller@gmx.de, daniel@ffwll.ch,
	sam@ravnborg.org, maxime@cerno.tech, linux-fbdev@vger.kernel.org,
	linux-staging@lists.linux.dev, dri-devel@lists.freedesktop.org,
	Zack Rusin <zackr@vmware.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Alex Deucher <alexander.deucher@amd.com>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	Changcheng Deng <deng.changcheng@zte.com.cn>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>
Subject: Re: [PATCH v2 07/11] video/aperture: Disable and unregister sysfb devices via aperture helpers
Date: Mon, 20 Mar 2023 10:46:56 +0100	[thread overview]
Message-ID: <e881f6d6-0d2b-5775-68f2-35cc4d666d63@suse.de> (raw)
In-Reply-To: <9f682c15a5484b4a94f63e20d41f67d0@cavoj.net>

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Hi

Am 20.03.23 um 02:47 schrieb Samuel Čavoj:
> Hi,
> 
>> diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
>> index f42a0d8bc211..101e13c2cf41 100644
>> --- a/drivers/video/aperture.c
>> +++ b/drivers/video/aperture.c
>> @@ -8,6 +8,7 @@
>>  #include <linux/pci.h>
>>  #include <linux/platform_device.h>
>>  #include <linux/slab.h>
>> +#include <linux/sysfb.h>
>>  #include <linux/types.h>
>>  #include <linux/vgaarb.h>
>>
>> @@ -286,7 +287,20 @@ int 
>> aperture_remove_conflicting_devices(resource_size_t base, 
>> resource_size_t si
>>  #if IS_REACHABLE(CONFIG_FB)
>>      struct apertures_struct *a;
>>      int ret;
>> +#endif
>> +
>> +    /*
>> +     * If a driver asked to unregister a platform device registered by
>> +     * sysfb, then can be assumed that this is a driver for a display
>> +     * that is set up by the system firmware and has a generic driver.
>> +     *
>> +     * Drivers for devices that don't have a generic driver will never
>> +     * ask for this, so let's assume that a real driver for the display
>> +     * was already probed and prevent sysfb to register devices later.
>> +     */
>> +    sysfb_disable();
> 
> This call to sysfb_disable() has been causing trouble with regard to
> VFIO. VFIO has been calling aperture_remove_conflicting_pci_devices to
> get rid of any console drivers (d173780620792c) using the device in
> question, but now even unrelated drivers are getting killed. Example
> situation:

Which drivers do you use?

Best regards
Thomas

> 
> Machine has two GPUs and uses efifb for the console. Efifb registers
> with the aperture system the efi framebuffer region, which is covered
> by a BAR resource of GPU 1. VFIO grabs GPU 2 and calls
> aperture_remove_conflicting_pci_devices(GPU 2). GPU 2 has no overlap
> with the efifb on GPU1 but the efifb is killed regardless due to
> the unconditional call to sysfb_disable(). The console switches
> to dummy and locks up from the user perspective.
> This seems unnecessary, as the device is unrelated.
> 
> I do not quite understand the comment justifying the call.
> 
> Some discussions with workarounds:
> https://old.reddit.com/r/VFIO/comments/11qei4t/framebuffer_doesnt_work_anymore_after_passthrough/
> https://bbs.archlinux.org/viewtopic.php?id=280512
> 
> 
> Thanks,
> Samuel

-- 
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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