[PATCH] drm/prime: Only call dma_map_sgtable() for devices with DMA support

[Thomas Zimmermann <tzimmermann@suse.de>]

Fixes a regression for udl and probably other USB-based drivers where
joining and mirroring displays fails.

Joining displays requires importing a dma_buf from another DRM driver.
These devices don't support DMA and therefore have no DMA mask. Trying
to map imported buffers from a DMA-able memory zone fails with an error.
An example is shown below.

[   60.050199] ------------[ cut here ]------------
[   60.055092] WARNING: CPU: 0 PID: 1403 at kernel/dma/mapping.c:190 dma_map_sg_attrs+0x8f/0xc0
[   60.064331] Modules linked in: af_packet(E) rfkill(E) dmi_sysfs(E) intel_rapl_msr(E) intel_rapl_common(E) snd_hda_codec_realtek(E) snd_hda_codec_generic(E) ledtrig_audio(E) snd_hda_codec_hdmi(E) x86_pkg_temp_thermal(E) intel_powerclam)
[   60.064801]  wmi(E) video(E) btrfs(E) blake2b_generic(E) libcrc32c(E) crc32c_intel(E) xor(E) raid6_pq(E) sg(E) dm_multipath(E) dm_mod(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) msr(E) efivarfs(E)
[   60.170778] CPU: 0 PID: 1403 Comm: Xorg.bin Tainted: G            E    5.11.0-rc5-1-default+ #747
[   60.179841] Hardware name: Dell Inc. OptiPlex 9020/0N4YC8, BIOS A24 10/24/2018
[   60.187145] RIP: 0010:dma_map_sg_attrs+0x8f/0xc0
[   60.191822] Code: 4d 85 ff 75 2b 49 89 d8 44 89 e1 44 89 f2 4c 89 ee 48 89 ef e8 62 30 00 00 85 c0 78 36 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 0b <0f> 0b 31 c0 eb ed 49 8d 7f 50 e8 72 f5 2a 00 49 8b 47 50 49 89 d8
[   60.210770] RSP: 0018:ffffc90001d6fc18 EFLAGS: 00010246
[   60.216062] RAX: 0000000000000000 RBX: 0000000000000020 RCX: ffffffffb31e677b
[   60.223274] RDX: dffffc0000000000 RSI: ffff888212c10600 RDI: ffff8881b08a9488
[   60.230501] RBP: ffff8881b08a9030 R08: 0000000000000020 R09: ffff888212c10600
[   60.237710] R10: ffffed10425820df R11: 0000000000000001 R12: 0000000000000000
[   60.244939] R13: ffff888212c10600 R14: 0000000000000008 R15: 0000000000000000
[   60.252155] FS:  00007f08ac2b2f00(0000) GS:ffff8887cbe00000(0000) knlGS:0000000000000000
[   60.260333] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   60.266150] CR2: 000055831c899be8 CR3: 000000015372e006 CR4: 00000000001706f0
[   60.273369] Call Trace:
[   60.275845]  drm_gem_map_dma_buf+0xb4/0x120
[   60.280089]  dma_buf_map_attachment+0x15d/0x1e0
[   60.284688]  drm_gem_prime_import_dev.part.0+0x5d/0x140
[   60.289984]  drm_gem_prime_fd_to_handle+0x213/0x280
[   60.294931]  ? drm_prime_destroy_file_private+0x30/0x30
[   60.300224]  drm_ioctl_kernel+0x131/0x180
[   60.304291]  ? drm_setversion+0x230/0x230
[   60.308366]  ? drm_prime_destroy_file_private+0x30/0x30
[   60.313659]  drm_ioctl+0x2f1/0x500
[   60.317118]  ? drm_version+0x150/0x150
[   60.320903]  ? lock_downgrade+0xa0/0xa0
[   60.324806]  ? do_vfs_ioctl+0x5f4/0x680
[   60.328694]  ? __fget_files+0x13e/0x210
[   60.332591]  ? ioctl_fiemap.isra.0+0x1a0/0x1a0
[   60.337102]  ? __fget_files+0x15d/0x210
[   60.340990]  __x64_sys_ioctl+0xb9/0xf0
[   60.344795]  do_syscall_64+0x33/0x80
[   60.348427]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   60.353542] RIP: 0033:0x7f08ac7b53cb
[   60.357168] Code: 89 d8 49 8d 3c 1c 48 f7 d8 49 39 c4 72 b5 e8 1c ff ff ff 85 c0 78 ba 4c 89 e0 5b 5d 41 5c c3 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 75 ba 0c 00 f7 d8 64 89 01 48
[   60.376108] RSP: 002b:00007ffeabc89fc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   60.383758] RAX: ffffffffffffffda RBX: 00007ffeabc8a00c RCX: 00007f08ac7b53cb
[   60.390970] RDX: 00007ffeabc8a00c RSI: 00000000c00c642e RDI: 000000000000000d
[   60.398221] RBP: 00000000c00c642e R08: 000055831c691d00 R09: 000055831b2ec010
[   60.405446] R10: 00007f08acf6ada0 R11: 0000000000000246 R12: 000055831c691d00
[   60.412667] R13: 000000000000000d R14: 00000000007e9000 R15: 0000000000000000
[   60.419903] irq event stamp: 672893
[   60.423441] hardirqs last  enabled at (672913): [<ffffffffb31b796d>] console_unlock+0x44d/0x500
[   60.432230] hardirqs last disabled at (672922): [<ffffffffb31b7963>] console_unlock+0x443/0x500
[   60.441021] softirqs last  enabled at (672940): [<ffffffffb46003dd>] __do_softirq+0x3dd/0x554
[   60.449634] softirqs last disabled at (672931): [<ffffffffb44010f2>] asm_call_irq_on_stack+0x12/0x20
[   60.458871] ---[ end trace f2f88696eb17806c ]---

For the fix, we don't call dma_map_sgtable() for devices without the
DMA mask. Drivers for such devices have to map the imported buffer into
kernel address space and perfom the copy operation in software.

Tested by joining/mirroring displays of udl and radeon un der Gnome/X11.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Johan Hovold <johan@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Oliver Neukum <oneukum@suse.com>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org> # v5.10+
---
 drivers/gpu/drm/drm_prime.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 2a54f86856af..d5a39fe76b78 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -603,10 +603,15 @@ EXPORT_SYMBOL(drm_gem_map_detach);
  * @attach: attachment whose scatterlist is to be returned
  * @dir: direction of DMA transfer
  *
- * Calls &drm_gem_object_funcs.get_sg_table and then maps the scatterlist. This
- * can be used as the &dma_buf_ops.map_dma_buf callback. Should be used together
+ * Calls &drm_gem_object_funcs.get_sg_table and, if possible, maps the scatterlist.
+ * This can be used as the &dma_buf_ops.map_dma_buf callback. Should be used together
  * with drm_gem_unmap_dma_buf().
  *
+ * Devices on some peripheral busses, such as USB, cannot use DMA. In this case,
+ * pages in the scatterlist remain unmapped. Drivers for such devices should acquire
+ * a mapping with dma_buf_vmap() and implement copy operation via bus-specific
+ * interfaces.
+ *
  * Returns:sg_table containing the scatterlist to be returned; returns ERR_PTR
  * on error. May return -EINTR if it is interrupted by a signal.
  */
@@ -627,12 +632,14 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
 	if (IS_ERR(sgt))
 		return sgt;

-	ret = dma_map_sgtable(attach->dev, sgt, dir,
-			      DMA_ATTR_SKIP_CPU_SYNC);
-	if (ret) {
-		sg_free_table(sgt);
-		kfree(sgt);
-		sgt = ERR_PTR(ret);
+	if (attach->dev->dma_mask) {
+		ret = dma_map_sgtable(attach->dev, sgt, dir,
+				      DMA_ATTR_SKIP_CPU_SYNC);
+		if (ret) {
+			sg_free_table(sgt);
+			kfree(sgt);
+			sgt = ERR_PTR(ret);
+		}
 	}

 	return sgt;
@@ -654,7 +661,9 @@ void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
 	if (!sgt)
 		return;

-	dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
+	if (attach->dev->dma_mask)
+		dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
+
 	sg_free_table(sgt);
 	kfree(sgt);
 }
--
2.30.0

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