Re: [REPOST PATCH] drm/msm: Set dma maximum segment size for mdss

From: Sai Prakash Ranjan
Date: Wed Jan 22 2020 - 09:14:47 EST

Hi,

On 2020-01-22 00:56, Rob Clark wrote:
On Tue, Jan 21, 2020 at 11:19 AM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:

From: Sean Paul <seanpaul@xxxxxxxxxxxx>

Turning on CONFIG_DMA_API_DEBUG_SG results in the following error:

[ 12.078665] msm ae00000.mdss: DMA-API: mapping sg segment longer than device claims to support [len=3526656] [max=65536]
[ 12.089870] WARNING: CPU: 6 PID: 334 at /mnt/host/source/src/third_party/kernel/v4.19/kernel/dma/debug.c:1301 debug_dma_map_sg+0x1dc/0x318
[ 12.102655] Modules linked in: joydev
[ 12.106442] CPU: 6 PID: 334 Comm: frecon Not tainted 4.19.0 #2
[ 12.112450] Hardware name: Google Cheza (rev3+) (DT)
[ 12.117566] pstate: 60400009 (nZCv daif +PAN -UAO)
[ 12.122506] pc : debug_dma_map_sg+0x1dc/0x318
[ 12.126995] lr : debug_dma_map_sg+0x1dc/0x318
[ 12.131487] sp : ffffff800cc3ba80
[ 12.134913] x29: ffffff800cc3ba80 x28: 0000000000000000
[ 12.140395] x27: 0000000000000004 x26: 0000000000000004
[ 12.145868] x25: ffffff8008e55b18 x24: 0000000000000000
[ 12.151337] x23: 00000000ffffffff x22: ffffff800921c000
[ 12.156809] x21: ffffffc0fa75b080 x20: ffffffc0f7195090
[ 12.162280] x19: ffffffc0f1c53280 x18: 0000000000000000
[ 12.167749] x17: 0000000000000000 x16: 0000000000000000
[ 12.173218] x15: 0000000000000000 x14: 0720072007200720
[ 12.178689] x13: 0720072007200720 x12: 0720072007200720
[ 12.184161] x11: 0720072007200720 x10: 0720072007200720
[ 12.189641] x9 : ffffffc0f1fc6b60 x8 : 0000000000000000
[ 12.195110] x7 : ffffff8008132ce0 x6 : 0000000000000000
[ 12.200585] x5 : 0000000000000000 x4 : ffffff8008134734
[ 12.206058] x3 : ffffff800cc3b830 x2 : ffffffc0f1fc6240
[ 12.211532] x1 : 25045a74f48a7400 x0 : 25045a74f48a7400
[ 12.217006] Call trace:
[ 12.219535] debug_dma_map_sg+0x1dc/0x318
[ 12.223671] get_pages+0x19c/0x20c
[ 12.227177] msm_gem_fault+0x64/0xfc
[ 12.230874] __do_fault+0x3c/0x140
[ 12.234383] __handle_mm_fault+0x70c/0xdb8
[ 12.238603] handle_mm_fault+0xac/0xc4
[ 12.242473] do_page_fault+0x1bc/0x3d4
[ 12.246342] do_translation_fault+0x54/0x88
[ 12.250652] do_mem_abort+0x60/0xf0
[ 12.254250] el0_da+0x20/0x24
[ 12.257317] irq event stamp: 67260
[ 12.260828] hardirqs last enabled at (67259): [<ffffff8008132d0c>] console_unlock+0x214/0x608
[ 12.269693] hardirqs last disabled at (67260): [<ffffff8008080e0c>] do_debug_exception+0x5c/0x178
[ 12.278820] softirqs last enabled at (67256): [<ffffff8008081664>] __do_softirq+0x4d4/0x520
[ 12.287510] softirqs last disabled at (67249): [<ffffff80080be574>] irq_exit+0xa8/0x100
[ 12.295742] ---[ end trace e63cfc40c313ffab ]---

The root of the problem is that the default segment size for sgt is
(UINT_MAX & PAGE_MASK), and the default segment size for device dma is
64K. As such, if you compare the 2, you would deduce that the sg segment
will overflow the device's capacity. In reality, the hardware can
accommodate the larger sg segments, it's just not initializing its max
segment properly. This patch initializes the max segment size for the
mdss device, which gets rid of that pesky warning.

Reported-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
Tested-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---
This patch has been floating in the ether for over a year [1]. I know
next to nothing about it, but I'm told it's still useful so I'm
helpfully reposting it. Please enjoy.

This looks like the right thing to do.. sorry I overlooked the patch
first time around

Reviewed-by: Rob Clark <robdclark@xxxxxxxxx>

(since I've already sent PR for msm-next, could we pick this up via drm-misc?)


This also fixes a similar warning seen on SC7180 during video playback.

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>

Logs for reference,

localhost ~ # [ 647.100504] ------------[ cut here ]------------
[ 647.105748] DMA-API: msm ae00000.mdss: mapping sg segment longer than device claims to support [len=524288] [max=65536]

<...snip...>

[ 647.184254] pstate: 60400009 (nZCv daif +PAN -UAO)
[ 647.189211] pc : debug_dma_map_sg+0x1a8/0x2c4
[ 647.193708] lr : debug_dma_map_sg+0x1a8/0x2c4
[ 647.198202] sp : ffffffc010f6ba80
[ 647.201626] x29: ffffffc010f6ba90 x28: 0000000000010000
[ 647.207110] x27: 00000000ffffffff x26: ffffff8174840b80
[ 647.212592] x25: ffffffe9f4fe5000 x24: 0000000000000003
[ 647.218075] x23: ffffff815c223780 x22: ffffff81742d0810
[ 647.223557] x21: 0000000000000003 x20: 0000000000000001
[ 647.229041] x19: 0000000000000001 x18: 0000000000000000
[ 647.234524] x17: 000000000000003c x16: ffffffe9f4444a14
[ 647.240006] x15: 0000000000000006 x14: 0720072007200720
[ 647.245489] x13: 0720072007200720 x12: 0000000000000000
[ 647.250969] x11: 0000000000000000 x10: 0000000000000000
[ 647.256452] x9 : 4be0233cf8ef6200 x8 : 4be0233cf8ef6200
[ 647.261935] x7 : 0720072007200720 x6 : ffffff8175ea0f00
[ 647.267417] x5 : 0000000000000000 x4 : 0000000000000000
[ 647.272898] x3 : 0000000000000000 x2 : ffffff81771d1680
[ 647.278380] x1 : ffffff81771c10c0 x0 : 000000000000006b
[ 647.283863] Call trace:
[ 647.286409] debug_dma_map_sg+0x1a8/0x2c4
[ 647.290569] vb2_dma_sg_dmabuf_ops_map+0x138/0x18c [videobuf2_dma_sg]
[ 647.297215] dma_buf_map_attachment+0x6c/0xb0
[ 647.301724] drm_gem_prime_import_dev+0xa4/0x134
[ 647.306495] drm_gem_prime_fd_to_handle+0xc4/0x194
[ 647.311444] drm_prime_fd_to_handle_ioctl+0x40/0x58
[ 647.316483] drm_ioctl_kernel+0x94/0x10c
[ 647.320538] drm_ioctl+0x264/0x3f8
[ 647.324059] drm_compat_ioctl+0xcc/0xdc
[ 647.328033] __se_compat_sys_ioctl+0x100/0x2074
[ 647.332715] __arm64_compat_sys_ioctl+0x20/0x2c
[ 647.337406] el0_svc_common+0xa4/0x154
[ 647.341279] el0_svc_compat_handler+0x2c/0x38
[ 647.345781] el0_svc_compat+0x8/0x10
[ 647.349474] ---[ end trace 2f188eb70b295b6c ]---
[ 648.282197] ------------[ cut here ]------------


Thanks,
Sai

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