[PATCH AUTOSEL 5.10 06/15] ata: libata-eh: Do not use ATAPI DMA for a device limited to PIO mode

Sasha Levin
2025-04-03T19:10:20Z

From: Niklas Cassel <cassel@kernel.org>

[ Upstream commit 91ec84f8eaddbc93d7c62e363d68aeb7b89879c7 ]

atapi_eh_request_sense() currently uses ATAPI DMA if the SATA controller
has ATA_FLAG_PIO_DMA (PIO cmds via DMA) set.

However, ATA_FLAG_PIO_DMA is a flag that can be set by a low-level driver
on a port at initialization time, before any devices are scanned.

If a controller detects a connected device that only supports PIO, we set
the flag ATA_DFLAG_PIO.

Modify atapi_eh_request_sense() to not use ATAPI DMA if the connected
device only supports PIO.

Reported-by: Philip Pemberton <lists@philpem.me.uk>
Closes: https://lore.kernel.org/linux-ide/c6722ee8-5e21-4169-af59-cbbae9edc02f@philpem.me.uk/
Tested-by: Philip Pemberton <lists@philpem.me.uk>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20250221015422.20687-2-cassel@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/ata/libata-eh.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 48130b2543966..e700024a8b482 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -1479,8 +1479,15 @@ unsigned int atapi_eh_request_sense(struct ata_device *dev,
tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
tf.command = ATA_CMD_PACKET;

- /* is it pointless to prefer PIO for "safety reasons"? */
- if (ap->flags & ATA_FLAG_PIO_DMA) {
+ /*
+ * Do not use DMA if the connected device only supports PIO, even if the
+ * port prefers PIO commands via DMA.
+ *
+ * Ideally, we should call atapi_check_dma() to check if it is safe for
+ * the LLD to use DMA for REQUEST_SENSE, but we don't have a qc.
+ * Since we can't check the command, perhaps we should only use pio?
+ */
+ if ((ap->flags & ATA_FLAG_PIO_DMA) && !(dev->flags & ATA_DFLAG_PIO)) {
tf.protocol = ATAPI_PROT_DMA;
tf.feature |= ATAPI_PKT_DMA;
} else {
--
2.39.5