From: Sam Day <me@samcday.com>

Currently, DMA_FROM_DEVICE is used when attaching DMABUFs to IN
endpoints and DMA_TO_DEVICE for OUT endpoints. This is inverted from
how it should be.

The result is IOMMU read-only mappings placed on OUT queues,
triggering arm-smmu write faults.

Put differently, OUT endpoints flow data from host -> gadget, meaning
the UDC peripheral needs to have write access to the buffer to fill it
with the incoming data.

This commit flips the directions and updates the implicit-sync helpers
so IN endpoints act as readers and OUT endpoints as writers.

Signed-off-by: Sam Day <me@samcday.com>
Tested-by: David Heidelberg <david@ixit.cz>  # OnePlus 6T on sdm845-next-20251119
---
 drivers/usb/gadget/function/f_fs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 9ea1445bec97531f9c2bed678268bd6f76199bfb..a738d835f61e3d6b31363ccb6dda563336996b0e 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1513,7 +1513,7 @@ static int ffs_dmabuf_attach(struct file *file, int fd)
 		goto err_dmabuf_detach;
 	}
 
-	dir = epfile->in ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+	dir = epfile->in ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
 
 	err = ffs_dma_resv_lock(dmabuf, nonblock);
 	if (err)
@@ -1643,7 +1643,7 @@ static int ffs_dmabuf_transfer(struct file *file,
 	/* Make sure we don't have writers */
 	timeout = nonblock ? 0 : msecs_to_jiffies(DMABUF_ENQUEUE_TIMEOUT_MS);
 	retl = dma_resv_wait_timeout(dmabuf->resv,
-				     dma_resv_usage_rw(epfile->in),
+				     dma_resv_usage_rw(!epfile->in),
 				     true, timeout);
 	if (retl == 0)
 		retl = -EBUSY;
@@ -1688,7 +1688,7 @@ static int ffs_dmabuf_transfer(struct file *file,
 	dma_fence_init(&fence->base, &ffs_dmabuf_fence_ops,
 		       &priv->lock, priv->context, seqno);
 
-	resv_dir = epfile->in ? DMA_RESV_USAGE_WRITE : DMA_RESV_USAGE_READ;
+	resv_dir = epfile->in ? DMA_RESV_USAGE_READ : DMA_RESV_USAGE_WRITE;
 
 	dma_resv_add_fence(dmabuf->resv, &fence->base, resv_dir);
 	dma_resv_unlock(dmabuf->resv);

-- 
2.52.0