Re: [PATCH v2] drm/sun4i: Add DMA mask and segment size

[Robin Murphy <robin.murphy@arm.com>]

On 2022-06-20 19:13, Jernej Skrabec wrote:
> Kernel occasionally complains that there is mismatch in segment size
> when trying to render HW decoded videos and rendering them directly with
> sun4i DRM driver. Following message can be observed on H6 SoC:
> 
> [  184.298308] ------------[ cut here ]------------
> [  184.298326] DMA-API: sun4i-drm display-engine: mapping sg segment longer than device claims to support [len=6144000] [max=65536]
> [  184.298364] WARNING: CPU: 1 PID: 382 at kernel/dma/debug.c:1162 debug_dma_map_sg+0x2b0/0x350
> [  184.322997] CPU: 1 PID: 382 Comm: ffmpeg Not tainted 5.19.0-rc1+ #1331
> [  184.329533] Hardware name: Tanix TX6 (DT)
> [  184.333544] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [  184.340512] pc : debug_dma_map_sg+0x2b0/0x350
> [  184.344882] lr : debug_dma_map_sg+0x2b0/0x350
> [  184.349250] sp : ffff800009f33a50
> [  184.352567] x29: ffff800009f33a50 x28: 0000000000010000 x27: ffff000001b86c00
> [  184.359725] x26: ffffffffffffffff x25: ffff000005d8cc80 x24: 0000000000000000
> [  184.366879] x23: ffff80000939ab18 x22: 0000000000000001 x21: 0000000000000001
> [  184.374031] x20: 0000000000000000 x19: ffff0000018a7410 x18: ffffffffffffffff
> [  184.381186] x17: 0000000000000000 x16: 0000000000000000 x15: ffffffffffffffff
> [  184.388338] x14: 0000000000000001 x13: ffff800009534e86 x12: 6f70707573206f74
> [  184.395493] x11: 20736d69616c6320 x10: 000000000000000a x9 : 0000000000010000
> [  184.402647] x8 : ffff8000093b6d40 x7 : ffff800009f33850 x6 : 000000000000000c
> [  184.409800] x5 : ffff0000bf997940 x4 : 0000000000000000 x3 : 0000000000000027
> [  184.416953] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff000003960e80
> [  184.424106] Call trace:
> [  184.426556]  debug_dma_map_sg+0x2b0/0x350
> [  184.430580]  __dma_map_sg_attrs+0xa0/0x110
> [  184.434687]  dma_map_sgtable+0x28/0x4c
> [  184.438447]  vb2_dc_dmabuf_ops_map+0x60/0xcc
> [  184.442729]  __map_dma_buf+0x2c/0xd4
> [  184.446321]  dma_buf_map_attachment+0xa0/0x130
> [  184.450777]  drm_gem_prime_import_dev+0x7c/0x18c
> [  184.455410]  drm_gem_prime_fd_to_handle+0x1b8/0x214
> [  184.460300]  drm_prime_fd_to_handle_ioctl+0x2c/0x40
> [  184.465190]  drm_ioctl_kernel+0xc4/0x174
> [  184.469123]  drm_ioctl+0x204/0x420
> [  184.472534]  __arm64_sys_ioctl+0xac/0xf0
> [  184.476474]  invoke_syscall+0x48/0x114
> [  184.480240]  el0_svc_common.constprop.0+0x44/0xec
> [  184.484956]  do_el0_svc+0x2c/0xc0
> [  184.488283]  el0_svc+0x2c/0x84
> [  184.491354]  el0t_64_sync_handler+0x11c/0x150
> [  184.495723]  el0t_64_sync+0x18c/0x190
> [  184.499397] ---[ end trace 0000000000000000 ]---
> 
> Fix that by setting DMA mask and segment size.
> 
> Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
> ---
> Changes from v1:
> - added comment
> - updated commit message with kernel report
> 
>   drivers/gpu/drm/sun4i/sun4i_drv.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_drv.c b/drivers/gpu/drm/sun4i/sun4i_drv.c
> index 275f7e4a03ae..f135a6b3cadb 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_drv.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_drv.c
> @@ -7,6 +7,7 @@
>    */
>   
>   #include <linux/component.h>
> +#include <linux/dma-mapping.h>
>   #include <linux/kfifo.h>
>   #include <linux/module.h>
>   #include <linux/of_graph.h>
> @@ -367,6 +368,13 @@ static int sun4i_drv_probe(struct platform_device *pdev)
>   
>   	INIT_KFIFO(list.fifo);
>   
> +	/*
> +	 * DE2 and DE3 cores actually supports 40-bit addresses, but
> +	 * driver does not.
> +	 */
> +	dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> +	dma_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32));

Nit: this one is a number, not a bitmask, so UINT_MAX would be more 
appropriate semantically.

Thanks,
Robin.

> +
>   	for (i = 0;; i++) {
>   		struct device_node *pipeline = of_parse_phandle(np,
>   								"allwinner,pipelines",