[PATCH 2/2] vkms: Add support for multiple connectors

Thu Apr 6 14:18:16 UTC 2023

Hi

Am 06.04.23 um 16:04 schrieb Marius Vlad:
[...]
> 
>>
>> For multiple outputs, you can attach multiple encoders/connectors to 
>> the same CRTC. They will then all display the same screen at the same 
>> display resolution
> Yeah, this kind of sounds like cloning to me, and would like to display 
> different things at the same time, on different outputs, to me it sounds 
> I need primary plane and a CRTC for each connector. Right?

Exactly.

Best regards
Thomas

> 
>>
>>> - Can the overlay planes be shared or I need to
>>>    discard the ones that are already in-use by other outputs?
>>
>> Even if your hardware planes support it, you cannot share planes among 
>> CRTCs with DRM. At least I'm not aware how to. Each plane struct has a 
>> designated CRTC struct. For most flexibility I'd have to match HW 
>> planes and DRM planes dynamically. For example if you have 2 CRTCs 
>> that can share 10 HW planes, you can allocate 10 DRM planes for each 
>> CRTC. The atomic_check functions have to implement the mapping from 
>> hardware to software plane and fail if no more hardware planes are 
>> available.
>>
>> If you want to display the same screen on multiple CRTCs, it's 
>> possible to share the DRM framebuffers among similar the planes.
> 
> Aham, understood, thanks again!
> 
>>
>> Best regards
>> Thomas
>>
>>>
>>> I'll have a look at that writeback test as well see what's causing that
>>> NULL pointer deref.
>>>
>>>
>>> On 4/5/23 16:51, Maíra Canal wrote:
>>>> Hi Marius,
>>>>
>>>>> This patch adds support for creating multiple virtual connectors, in
>>>>> case one would need it. Use module parameters to specify how many,
>>>>> defaulting to just one, allocating from the start, a maximum of 4
>>>>> possible outputs.
>>>>
>>>> I got a bit confused by this description. The commit message says 
>>>> that you
>>>> are creating multiple connectors, but it seems like you are creating 
>>>> multiple
>>>> pipes. From what I could see, for each new connector created, you 
>>>> are also
>>>> creating a new CRTC and new planes.
>>>>
>>>> Moreover, if your real intention is to create multiple pipes, I 
>>>> believe that
>>>> you don't really need to duplicate the planes as well.
>>>>
>>>> I ran the VKMS CI [1] with your patches applied and, although most 
>>>> of the
>>>> tests are now passing with multiple pipes, which is really nice, the 
>>>> test
>>>> kms_writeback crashes with the following error:
>>>>
>>>> [ 1997.244347] [IGT] kms_writeback: starting subtest 
>>>> writeback-check-output
>>>> [ 1997.250673] BUG: kernel NULL pointer dereference, address: 
>>>> 000000000000016c
>>>> [ 1997.250691] #PF: supervisor read access in kernel mode
>>>> [ 1997.250693] #PF: error_code(0x0000) - not-present page
>>>> [ 1997.250694] PGD 800000001a877067 P4D 800000001a877067 PUD 
>>>> 1a872067 PMD 0
>>>> [ 1997.250697] Oops: 0000 [#1] PREEMPT SMP PTI
>>>> [ 1997.250699] CPU: 2 PID: 3223 Comm: kms_writeback Not tainted 
>>>> 6.3.0-rc4-g8c2c29ba129f-dirty #257
>>>> [ 1997.250701] Hardware name: QEMU Standard PC (i440FX + PIIX, 
>>>> 1996), BIOS 1.16.2-1.fc37 04/01/2014
>>>> [ 1997.250703] RIP: 0010:drm_vblank_get+0xa/0xe0
>>>> [ 1997.250710] Code: a9 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 
>>>> 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 41 57 41 56 41 55 
>>>> 41 54 53 <8b> 87 6c 01 00 00 41 bc ea ff ff ff 85 c0 74 74 89 f5 48 
>>>> 89 fb 39
>>>> [ 1997.250712] RSP: 0018:ffffb84d407a3b08 EFLAGS: 00010202
>>>> [ 1997.250714] RAX: 0000000000000000 RBX: ffffa2eb02bf8b70 RCX: 
>>>> 0000000000000000
>>>> [ 1997.250718] RDX: ffffa2eb180d2420 RSI: 0000000000000000 RDI: 
>>>> 0000000000000000
>>>> [ 1997.250719] RBP: ffffa2eb02bf99e8 R08: 0000000000000036 R09: 
>>>> ffffa2eb01d620c0
>>>> [ 1997.250720] R10: ffffe82b84027e40 R11: ffffffffc0042520 R12: 
>>>> ffffa2eb01c01900
>>>> [ 1997.250721] R13: ffffa2eb02bf9b60 R14: 0000000000000001 R15: 
>>>> ffffa2ea1ecd6b80
>>>> [ 1997.250722] FS:  00007f7d44e89a80(0000) GS:ffffa2eb3bd00000(0000) 
>>>> knlGS:0000000000000000
>>>> [ 1997.250723] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> [ 1997.250725] CR2: 000000000000016c CR3: 000000001ec02000 CR4: 
>>>> 00000000000006e0
>>>> [ 1997.250728] Call Trace:
>>>> [ 1997.250735]  <TASK>
>>>> [ 1997.250736]  vkms_set_composer+0x18/0x60 [vkms]
>>>> [ 1997.250745]  vkms_wb_atomic_commit+0x93/0x150 [vkms]
>>>> [ 1997.250749]  drm_atomic_helper_commit_modeset_enables+0x1d9/0x250
>>>> [ 1997.250754]  vkms_atomic_commit_tail+0x33/0xb0 [vkms]
>>>> [ 1997.250758]  commit_tail+0x8d/0x170
>>>> [ 1997.250761]  drm_atomic_helper_commit+0x26b/0x280
>>>> [ 1997.250763]  drm_atomic_commit+0x9f/0xc0
>>>> [ 1997.250766]  ? __pfx___drm_printfn_info+0x10/0x10
>>>> [ 1997.250769]  drm_mode_atomic_ioctl+0x34c/0x480
>>>> [ 1997.250771]  ? __pfx_drm_mode_atomic_ioctl+0x10/0x10
>>>> [ 1997.250773]  drm_ioctl_kernel+0xd7/0x150
>>>> [ 1997.250780]  drm_ioctl+0x31f/0x490
>>>> [ 1997.250781]  ? __pfx_drm_mode_atomic_ioctl+0x10/0x10
>>>> [ 1997.250783]  __se_sys_ioctl+0x6d/0xb0
>>>> [ 1997.250789]  do_syscall_64+0x43/0x90
>>>> [ 1997.250795]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
>>>>
>>>> [1] 
>>>> https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/tree/master/tests/vkms_ci
>>>>
>>>> Best Regards,
>>>> - Maíra Canal
>>>>
>>>>>
>>>>> This is of particular importance when testing out the DRM backend in
>>>>> compositors, but also to be able to independently handle multiple
>>>>> outputs/connectors, like setting one to off/sleep on while the others
>>>>> are on, and combinations that arise from that.
>>>>>
>>>>> Signed-off-by: Marius Vlad <marius.vlad at collabora.com>
>>>>> ---
>>>>>   drivers/gpu/drm/vkms/vkms_crtc.c      |  3 +--
>>>>>   drivers/gpu/drm/vkms/vkms_drv.c       | 26 
>>>>> ++++++++++++++++++++++----
>>>>>   drivers/gpu/drm/vkms/vkms_drv.h       |  8 +++++---
>>>>>   drivers/gpu/drm/vkms/vkms_output.c    |  5 ++---
>>>>>   drivers/gpu/drm/vkms/vkms_writeback.c | 18 ++++++++----------
>>>>>   5 files changed, 38 insertions(+), 22 deletions(-)
>>>>>
>>

-- 
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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