On 10/30/2026 7:27 PM, Igor Opaniuk wrote:
SDHCI_QUIRK_WAIT_SEND_CMD makes sdhci_send_command() sleep for 1 ms
after every command. msm_sdhci has set it since the driver was added
for APQ8016, back when it only did PIO; the commit gives no reason for
it, and the Linux sdhci-msm driver has no such delay.
The delay is invisible for large reads but dominates small ones. A
multi-block read is CMD18 followed by CMD12, so every read pays 2 ms
on top of the transfer. With the eMMC in HS400 a 128 KiB read takes
about 0.4 ms, so USB mass storage, which reads in 128 KiB (FSG_BUFLEN)
chunks, spent most of its time in udelay(). On the Arduino UNO Q,
reading 1 GiB from "ums 0 mmc 0" on a USB 3 host
(dd if=/dev/sdX of=/dev/null bs=4M count=256):
host throughput time in eMMC reads (10.6k reads)
with the quirk 46 MB/s 26.8 s (~2.5 ms per read)
without 201 MB/s 4.5 s (~0.4 ms per read)
A single 128 MiB "mmc read" runs at 255.6 MiB/s either way.
Drop the quirk and keep SDHCI_QUIRK_BROKEN_R1B.
Tested on the Arduino UNO Q (QRB2210, qcom,sdhci-msm-v5, ADMA):
- on main (eMMC in DDR52): 128 MiB "mmc read" at 75 MiB/s as before,
the CRC32 of the first 128 MiB read in U-Boot matches the one Linux
computes from the same blocks, and Linux boots from the eMMC;
- with the "qcom: Enable HS200/HS400 eMMC modes" series and the
mass_storage SuperSpeed descriptor patch applied (eMMC in HS400):
the ums numbers above, same CRC32 check and Linux boot.
Not tested on v4 controllers or on the boards that use the driver in
PIO mode (qcom_dragonboard410c, qcom_dragonboard820c, hmibsc).
Signed-off-by: Igor Opaniuk <[email protected]>
---
Drop the 1 ms delay msm_sdhci adds after every SD command. It costs
2 ms per multi-block read, which capped ums on an Arduino UNO Q at
46 MB/s; without it the same read runs at 201 MB/s.
Testing on APQ8016/APQ8096 (PIO mode) would be welcome.
---
drivers/mmc/msm_sdhci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/mmc/msm_sdhci.c b/drivers/mmc/msm_sdhci.c
index 9cc11a5e269..ab217393a54 100644
--- a/drivers/mmc/msm_sdhci.c
+++ b/drivers/mmc/msm_sdhci.c
@@ -198,7 +198,7 @@ static int msm_sdc_probe(struct udevice *dev)
udelay(200);
}
- host->quirks = SDHCI_QUIRK_WAIT_SEND_CMD | SDHCI_QUIRK_BROKEN_R1B;
+ host->quirks = SDHCI_QUIRK_BROKEN_R1B;
host->max_clk = 0;
---
base-commit: 3973f3c4d24df75ca90d7c0a9f03e5e5c9b48f32
change-id: 20261030-msm-sdhci-wait-send-cmd-4383f2792022
Best regards,
Reviewed-by: Aswin Murugan <[email protected]>
