On 2020-12-22 10:21, Kiwoong Kim wrote:
Exynos requires one scatterlist entry for smaller than
page size, i.e. 4KB. For the cases of dispatching commands
with more than one scatterlist entry and under 4KB size,
Exynos behaves as follows:
Given that a command to read something
from device is dispatched with two scatterlist entries that
are named AAA and BBB. After dispatching, host builds two PRDT
entries and during transmission, device sends just one DATA IN
because device doesn't care on host dma.
If my understanding is correct, above is same to all hosts, only
below part is Exynos's behavior. Please correct me if I am wrong.
The host then tranfers
the whole data from start address of the area named AAA.
In consequebnce, the area that follows AAA would be corrupted.
In consequence
|<------------->|
+-------+------------ +-------+
+ AAA + (corrupted) ... + BBB +
+-------+------------ +-------+
AFAIK, queue->dma_alignment is only used in the case of direct-io,
i.e. in blk_rq_map_user/kern(), which are mainly used in IOCTL.
If a request's buffer len and/or buffer start addr is not aligned
with queue->dma_alignment, bio.c will make a bounce bio such that
the request get a new buffer which starts on a new page. After the
bounce bio is ended, the data in the bound bio will be copied to the
initial buffer.
So in this fix, you are making sure the AAA and BBB are all mapped to
one bounce bio and stay in one bi_vec, so when we do map_sg they come
in one sglist, please correct me if I am wrong.
If my understanding is correct, what is the real use case here -
why/how user starts a request which can generate more than one
sglists whose sizes are all under 4KB? I am just curious.
Thanks,
Can Guo.
Signed-off-by: Kiwoong Kim <kwmad.kim@xxxxxxxxxxx>
---
drivers/scsi/ufs/ufs-exynos.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/scsi/ufs/ufs-exynos.c
b/drivers/scsi/ufs/ufs-exynos.c
index a8770ff..8635d9d 100644
--- a/drivers/scsi/ufs/ufs-exynos.c
+++ b/drivers/scsi/ufs/ufs-exynos.c
@@ -14,6 +14,7 @@
#include <linux/of_address.h>
#include <linux/phy/phy.h>
#include <linux/platform_device.h>
+#include <linux/blkdev.h>
#include "ufshcd.h"
#include "ufshcd-pltfrm.h"
@@ -1193,6 +1194,13 @@ static int exynos_ufs_resume(struct ufs_hba
*hba, enum ufs_pm_op pm_op)
return 0;
}
+static void exynos_ufs_slave_configure(struct scsi_device *sdev)
+{
+ struct request_queue *q = sdev->request_queue;
+
+ blk_queue_update_dma_alignment(q, PAGE_SIZE - 1);
+}
+
static struct ufs_hba_variant_ops ufs_hba_exynos_ops = {
.name = "exynos_ufs",
.init = exynos_ufs_init,
@@ -1204,6 +1212,7 @@ static struct ufs_hba_variant_ops
ufs_hba_exynos_ops = {
.hibern8_notify = exynos_ufs_hibern8_notify,
.suspend = exynos_ufs_suspend,
.resume = exynos_ufs_resume,
+ .slave_configure = exynos_ufs_slave_configure,
};
static int exynos_ufs_probe(struct platform_device *pdev)
