Hi Noralf Am 07.10.23 um 14:01 schrieb Noralf Trønnes:
On 10/5/23 11:04, Thomas Zimmermann wrote:DRM's format-conversion helpers require temporary memory. Pass the buffer from the caller and keep it allocated over several calls. Allow the caller to preallocate the buffer memory. The motivation for this patchset is the recent work on a DRM panic handler. [1] The panic handler requires format conversion to display an error to the screen. But allocating memory during kernel panics is fragile. The changes in this patchset enable the DRM panic handler to preallocate buffer storage before the panic occurs.I've been thinking about this and afaiu this requires the display hw to switch to the new panic buffer for scanout, right? I don't think that is possible for any complex hw to do in a panic situation. Or are you thinking that the driver should somehow "memcpy" this buffer to the actual scanout buffer?
It's all of that, but depends on the situation. In the easy case, we have a usable scanout buffer during the panic (e.g., XRGB888). We can use it for the panic screen.
If there's no such scanout programmed, we can attempt to set a new display mode. I think, it is best to leave these exact steps to the DRM driver. Some drivers might not be able to reprogram the display (e.g., with USB or I2C hardware).
In the panic handler, we copy glyphs into the scanout buffer and possibly convert the color format during that process. Without a working scanout buffer, the panic handler does nothing.
Best regards Thomas
Noralf.As an additonal benefit, drivers can now keep the temporary storage across multiple updates. Avoiding memory allocation slightly reduces the CPU overhead of the format helpers. Patch 1 adds struct drm_format_conv_state, a simple interface to pass around the buffer storage. Patch 2 adds an instance of the struct to the shadow-plane state. Patch 3 moves the buffer's memory management from the format helpers into their callers within the DRM drivers. Most of the afected drivers use the state instance stored in their shadow- plane state. The shadow-plane code releases the buffer memory automatically. Patches 4 to 7 update three drivers to preallocate the format-conversion buffer in their plane's atomic_check function. The driver thus detects OOM errors before the display update begins. Tested with simpledrm. v4: * rename struct to drm_format_conv_state (Javier) * replace ARRAY_SIZE() with sizeof() (Jani) * store buffer in shadow-plane state (Javier, Maxime) * prealloc in atomic_check in several drivers v3: * no changes v2: * reserve storage during probing in the drivers [1] https://patchwork.freedesktop.org/series/122244/ Thomas Zimmermann (7): drm/format-helper: Cache buffers with struct drm_format_conv_state drm/atomic-helper: Add format-conversion state to shadow-plane state drm/format-helper: Pass format-conversion state to helpers drm/ofdrm: Preallocate format-conversion buffer in atomic_check drm/simpledrm: Preallocate format-conversion buffer in atomic_check drm/ssd130x: Fix atomic_check for disabled planes drm/ssd130x: Preallocate format-conversion buffer in atomic_check drivers/gpu/drm/drm_format_helper.c | 212 +++++++++++++----- drivers/gpu/drm/drm_gem_atomic_helper.c | 9 + drivers/gpu/drm/drm_mipi_dbi.c | 19 +- drivers/gpu/drm/gud/gud_pipe.c | 30 ++- drivers/gpu/drm/solomon/ssd130x.c | 36 ++- .../gpu/drm/tests/drm_format_helper_test.c | 72 +++--- drivers/gpu/drm/tiny/cirrus.c | 3 +- drivers/gpu/drm/tiny/ili9225.c | 10 +- drivers/gpu/drm/tiny/ofdrm.c | 16 +- drivers/gpu/drm/tiny/repaper.c | 8 +- drivers/gpu/drm/tiny/simpledrm.c | 43 +++- drivers/gpu/drm/tiny/st7586.c | 19 +- include/drm/drm_format_helper.h | 81 +++++-- include/drm/drm_gem_atomic_helper.h | 10 + include/drm/drm_mipi_dbi.h | 4 +- 15 files changed, 428 insertions(+), 144 deletions(-) base-commit: 57d3b83a83c5527325efb5bcaf594da09fe4a41b
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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