linux-toradex.git/drivers/video/fbdev/udlfb.c, branch v4.19

udlfb: use spin_lock_irq instead of spin_lock_irqsave

2018-07-25T13:41:57+00:00

spin_lock_irqsave and spin_unlock_irqrestore is inteded to be called from
a context where it is unknown if interrupts are enabled or disabled (such
as interrupt handlers). From a process context, we should call
spin_lock_irq and spin_unlock_irq, that avoids the costly pushf and popf
instructions.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: avoid prefetch

2018-07-25T13:41:57+00:00

Modern processors can detect linear memory accesses and prefetch data
automatically, so there's no need to use prefetch.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: optimization - test the backing buffer

2018-07-25T13:41:56+00:00

Currently, the udlfb driver only tests for identical bytes at the
beginning or at the end of a page and renders anything between the first
and last mismatching pixel. But pages are not the same as lines, so this
is quite suboptimal - if there is something modified at the beginning of a
page and at the end of a page, the whole page is rendered, even if most of
the page is not modified.

This patch makes it test for identical pixels at the beginning and end of
each rendering command. This patch improves identical byte detection by
41% when playing video in a window.

This patch also fixes a possible screen corruption if the user is writing
to the framebuffer while dlfb_render_hline is in progress - the pixel data
that is copied to the backbuffer with memcpy may be different from the
pixel data that is actually rendered to the hardware (because the content
of the framebuffer may change between memcpy and the rendering command).
We must make sure that we copy exactly the same pixel as the pixel that is
being rendered.

Signed-off-by: Mikulas Patocka 
[b.zolnierkie: fix code indent]
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: allow reallocating the framebuffer

2018-07-25T13:41:56+00:00

This patch changes udlfb so that it may reallocate the framebuffer when
setting higher-resolution mode. If we boot the system without monitor
attached, udlfb creates a framebuffer with the size 800x600. This patch
makes it possible to select higher videomode with the fbset command when
a monitor is attached.

Note that there is no reliable way to prevent the system from touching the
old framebuffer, so we must not free it. We add it to the list
dlfb->deferred_free and free it when the driver is unloaded.

Signed-off-by: Mikulas Patocka 
[b.zolnierkie: sparse fixes]
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: set line_length in dlfb_ops_set_par

2018-07-25T13:41:56+00:00

Set the variable "line_length" in the function dlfb_ops_set_par. Without
this, we get garbage if we select different videomode with fbset.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: handle allocation failure

2018-07-25T13:41:56+00:00

Allocations larger than PAGE_ALLOC_COSTLY_ORDER are unreliable and they
may fail anytime. This patch fixes the udlfb driver so that when a large
alloactions fails, it tries to do multiple smaller allocations.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: make a local copy of fb_ops

2018-07-25T13:41:55+00:00

The defio subsystem overwrites the method fb_osp->mmap. That method is
stored in module's static data - and that means that if we have multiple
diplaylink adapters, they will over write each other's method.

In order to avoid interference between multiple adapters, we copy the
fb_ops structure to a device-local memory.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: don't switch if we are switching to the same videomode

2018-07-25T13:41:55+00:00

The udlfb driver reprograms the hardware everytime the user switches the
console, that makes quite unusable when working on the console.

This patch makes the driver remember the videomode we are in and avoid
reprogramming the hardware if we switch to the same videomode.

We mask the "activate" field and the "FB_VMODE_SMOOTH_XPAN" flag when
comparing the videomode, because they cause spurious switches when
switching to and from the Xserver.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: fix display corruption of the last line

2018-07-25T13:41:54+00:00

The displaylink hardware has such a peculiarity that it doesn't render a
command until next command is received. This produces occasional
corruption, such as when setting 22x11 font on the console, only the first
line of the cursor will be blinking if the cursor is located at some
specific columns.

When we end up with a repeating pixel, the driver has a bug that it leaves
one uninitialized byte after the command (and this byte is enough to flush
the command and render it - thus it fixes the screen corruption), however
whe we end up with a non-repeating pixel, there is no byte appended and
this results in temporary screen corruption.

This patch fixes the screen corruption by always appending a byte 0xAF at
the end of URB. It also removes the uninitialized byte.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
Signed-off-by: Bartlomiej Zolnierkiewicz

udlfb: fix semaphore value leak

2018-07-25T13:41:54+00:00

I observed that the performance of the udl fb driver degrades over time.
On a freshly booted machine, it takes 6 seconds to do "ls -la /usr/bin";
after some time of use, the same operation takes 14 seconds.

The reason is that the value of "limit_sem" decays over time.

The udl driver uses a semaphore "limit_set" to specify how many free urbs
are there on dlfb->urbs.list. If the count is zero, the "down" operation
will sleep until some urbs are added to the freelist.

In order to avoid some hypothetical deadlock, the driver will not call
"up" immediately, but it will offload it to a workqueue. The problem is
that if we call "schedule_delayed_work" on the same work item multiple
times, the work item may only be executed once.

This is happening:
* some urb completes
* dlfb_urb_completion adds it to the free list
* dlfb_urb_completion calls schedule_delayed_work to schedule the function
  dlfb_release_urb_work to increase the semaphore count
* as the urb is on the free list, some other task grabs it and submits it
* the submitted urb completes, dlfb_urb_completion is called again
* dlfb_urb_completion calls schedule_delayed_work, but the work is already
  scheduled, so it does nothing
* finally, dlfb_release_urb_work is called, it increases the semaphore
  count by 1, although it should increase it by 2

So, the semaphore count is decreasing over time, and this causes gradual
performance degradation.

Note that in the current kernel, the "up" function may be called from
interrupt and it may race with the "down" function called by another
thread, so we don't have to offload the call of "up" to a workqueue at
all. This patch removes the workqueue code. The patch also changes
"down_interruptible" to "down" in dlfb_free_urb_list, so that we will
clean up the driver properly even if a signal arrives.

With this patch, the performance of udlfb no longer degrades.

Signed-off-by: Mikulas Patocka 
Cc: stable@vger.kernel.org
[b.zolnierkie: fix immediatelly -> immediately typo]
Signed-off-by: Bartlomiej Zolnierkiewicz