Am 13.03.19 um 16:38 schrieb Michel Dänzer:
On 2019-03-13 2:37 p.m., Christian König wrote:
Am 13.03.19 um 14:31 schrieb Ville Syrjälä:
On Wed, Mar 13, 2019 at 10:35:08AM +0100, Michel Dänzer wrote:
On 2019-03-12 6:15 p.m., Noralf Trønnes wrote:
Den 12.03.2019 17.17, skrev Ville Syrjälä:
On Tue, Mar 12, 2019 at 11:47:04AM +0100, Michel Dänzer wrote:
On 2019-03-11 6:42 p.m., Noralf Trønnes wrote:
This adds support for outputting kernel messages on panic().
A kernel message dumper is used to dump the log. The dumper iterates
over each DRM device and it's crtc's to find suitable framebuffers.
All the other dumpers are run before this one except mtdoops.
Only atomic drivers are supported.
Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
---
[...]
diff --git a/include/drm/drm_framebuffer.h
b/include/drm/drm_framebuffer.h
index f0b34c977ec5..f3274798ecfe 100644
--- a/include/drm/drm_framebuffer.h
+++ b/include/drm/drm_framebuffer.h
@@ -94,6 +94,44 @@ struct drm_framebuffer_funcs {
struct drm_file *file_priv, unsigned flags,
unsigned color, struct drm_clip_rect *clips,
unsigned num_clips);
+
+ /**
+ * @panic_vmap:
+ *
+ * Optional callback for panic handling.
+ *
+ * For vmapping the selected framebuffer in a panic context.
Must
+ * be super careful about locking (only trylocking allowed).
+ *
+ * RETURNS:
+ *
+ * NULL if it didn't work out, otherwise an opaque cookie
which is
+ * passed to @panic_draw_xy. It can be anything: vmap area,
structure
+ * with more details, just a few flags, ...
+ */
+ void *(*panic_vmap)(struct drm_framebuffer *fb);
FWIW, the panic_vmap hook cannot work in general with the
amdgpu/radeon
drivers:
Framebuffers are normally tiled, writing to them with the CPU
results in
garbled output.
In which case the driver needs to support the ->panic_draw_xy callback,
or maybe it's possible to make a generic helper for tiled buffers.
I'm afraid that won't help, at least not without porting big chunks of
https://gitlab.freedesktop.org/mesa/mesa/tree/master/src/amd/addrlib
into the kernel, none of which will be used for anything else.
There would need to be a mechanism for switching scanout to a linear,
CPU accessible framebuffer.
I suppose panic_vmap() could just provide a linear temp buffer
to the panic handler, and panic_unmap() could copy the contents
over to the real fb.
Copy how? Using a GPU engine?
CPU maybe? Though I suppose that won't work if the buffer isn't CPU
accesible :/
Well we do have a debug path for accessing invisible memory with the CPU.
E.g. three registers: DATA and auto increment OFFSET_LO/HI. So you can
just read/write DATA over and over again if you want to access some memory.
Right. I assume that'll be very slow, but I guess it could do when the
memory isn't directly CPU accessible.
Just made a quick test and reading 33423360 bytes (4096x2040x4) using
that interfaces takes about 13 seconds.
IIRC we don't use the auto increment optimization yet, so that can
probably be improved by a factor of 3 or more.
But turning of tilling etc is still extremely tricky when the system is
already unstable.
Maybe we could add a little hook to the display code, which just
disables tiling for scanout and maybe disables non-primary planes, but
doesn't touch anything else. Harry / Nicholas, does that seem feasible?
I'm coming around from "this is never going to work" to "it might
actually work" with our hardware...
Yeah, agree. It's a bit tricky, but doable.
Takeaway for Noralf is that this whole vmap on panic won't even remotely
work. We need to get the data byte by byte without a page mapping if
that is ever going to fly.
Christian.
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