I'm pretty sure udlkms handles this already.
Dave.
On Wed, Aug 1, 2018 at 11:34 PM, Mikulas Patocka <mpato...@redhat.com>
wrote:
>
>
> On Wed, 1 Aug 2018, Geert Uytterhoeven wrote:
>
> > Hi Mikulas,
> >
> > On Wed, Aug 1, 2018 at 12:59 PM Mikulas Patocka <mpato...@redhat.com>
> wrote:
> > > On Wed, 1 Aug 2018, Geert Uytterhoeven wrote:
> > > > On Tue, Jul 31, 2018 at 5:23 PM Mikulas Patocka <mpato...@redhat.com>
> wrote:
> > > > > BTW when using the udlfb driver as a console, I've got this
> warning.
> > > > > vt_console_print takes a spinlock and then calls the framebuffer
> driver
> > > > > that sleeps.
> > > > >
> > > > > The question is - whose fault is this? Could the console code
> somehow be
> > > > > told to print characters without holding a spinlock? Or does it
> mean that
> > > > > framebuffer drivers can't sleep?
> > > > >
> > > > > udlfb communicates through USB, so the sleeping is inevitable.
> > > > >
> > > > > Mikulas
> > > > >
> > > > >
> > > > > BUG: sleeping function called from invalid context at mm/slab.h:421
> > > > > in_atomic(): 1, irqs_disabled(): 0, pid: 430, name: kworker/2:3
> > > > > 6 locks held by kworker/2:3/430:
> > > > > #0: 000000001301127e ( (wq_completion)"events"){....} , at:
> process_one_work+0x17c/0x3a8
> > > > > #1: 00000000beacc951 ( (work_completion)(&(&dlfb->
> init_framebuffer_work)->work)){....} , at: process_one_work+0x17c/0x3a8
> > > > > #2: 00000000a402f826 ( registration_lock){....} , at:
> register_framebuffer+0x28/0x2c0 [fb]
> > > > > #3: 0000000021cbe902 ( console_lock){....} , at:
> register_framebuffer+0x258/0x2c0 [fb]
> > > > > #4: 0000000096d51735 ( console_owner){....} , at:
> console_unlock+0x174/0x500
> > > > > #5: 00000000faa7f206 ( printing_lock){....} , at:
> vt_console_print+0x60/0x3a0
> > > > > Preemption disabled at: [<ffffff8008403130>]
> vt_console_print+0x60/0x3a0
> > > > > CPU: 2 PID: 430 Comm: kworker/2:3 Not tainted 4.17.10-debug #3
> > > > > Hardware name: Marvell Armada 8040 MacchiatoBin/Armada 8040
> MacchiatoBin, BIOS EDK II Jul 30 2018
> > > > > Workqueue: events dlfb_init_framebuffer_work [udlfb]
> > > > > Call trace:
> > > > > dump_backtrace+0x0/0x150
> > > > > show_stack+0x14/0x20
> > > > > dump_stack+0x8c/0xac
> > > > > ___might_sleep+0x140/0x170
> > > > > __might_sleep+0x50/0x88
> > > > > __kmalloc+0x1b0/0x270
> > > > > xhci_urb_enqueue+0xa8/0x460 [xhci_hcd]
> > > > > usb_hcd_submit_urb+0xc0/0x998 [usbcore]
> > > > > usb_submit_urb+0x1e0/0x518 [usbcore]
> > > > > dlfb_submit_urb+0x38/0x98 [udlfb]
> > > > > dlfb_handle_damage.isra.4+0x1e0/0x210 [udlfb]
> > > > > dlfb_ops_imageblit+0x28/0x38 [udlfb]
> > > > > soft_cursor+0x15c/0x1d8 [fb]
> > > > > bit_cursor+0x324/0x510 [fb]
> > > > > fbcon_cursor+0x144/0x1a0 [fb]
> > > > > hide_cursor+0x38/0xa0
> > > > > vt_console_print+0x334/0x3a0
> > > > > console_unlock+0x274/0x500
> > > > > register_framebuffer+0x22c/0x2c0 [fb]
> > > > > dlfb_init_framebuffer_work+0x1ec/0x2fc [udlfb]
> > > > > process_one_work+0x1e8/0x3a8
> > > > > worker_thread+0x44/0x418
> > > > > kthread+0x11c/0x120
> > > > > ret_from_fork+0x10/0x18
> > > >
> > > > This is sort of expected: you cannot do USB transfers from printk().
> > > >
> > > > Gr{oetje,eeting}s,
> > > >
> > > > Geert
> > >
> > > So, should there be a framebuffer flag that prevents the console from
> > > binding to it?
> > >
> > > If I start the kernel with "console=ttyS0,115200", it doesn't try to
> bind
> > > to the udlfb driver, but if I start it without this flag, it does and
> > > crashes :-(
> >
> > Your frame buffer driver should offload tasks that may sleep to e.g. a
> > workqueue.
> >
> > Gr{oetje,eeting}s,
> >
> > Geert
>
> I can try to do this - but - taking a spinlock and copying 8MB framebuffer
> would damage scheduling latency even for PCI framebuffer drivers.
>
> Mikulas
>
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