sdhci-of-dwcmshc meets an eMMC read performance regression with below
command after commit 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto
Select support"):
dd if=/dev/mmcblk0 of=/dev/null bs=8192 count=100000
Before the commit, the above command gives 120MB/s
After the commit, the above command gives 51.3 MB/s
So it looks like sdhci-of-dwcmshc expects Version 4 Mode for Auto
CMD Auto Select. Fix the performance degradation by ensuring v4_mode
is true to use Auto CMD Auto Select.
Fixes: 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto Select support")
Signed-off-by: Jisheng Zhang <jisheng.zh...@synaptics.com>
---
Since v1:
- add the performance degradation on sdhci-of-dwcmshc explanation in
commit msg
- add a comment in the code explaining we require Version 4 Mode because some
controllers(e.g sdhci-of-dwcmshc) expect it that way.
drivers/mmc/host/sdhci.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 592a55a34b58..3561ae8a481a 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1384,9 +1384,11 @@ static inline void sdhci_auto_cmd_select(struct
sdhci_host *host,
/*
* In case of Version 4.10 or later, use of 'Auto CMD Auto
* Select' is recommended rather than use of 'Auto CMD12
- * Enable' or 'Auto CMD23 Enable'.
+ * Enable' or 'Auto CMD23 Enable'. We require Version 4 Mode
+ * here because some controllers (e.g sdhci-of-dwmshc) expect it.
*/
- if (host->version >= SDHCI_SPEC_410 && (use_cmd12 || use_cmd23)) {
+ if (host->version >= SDHCI_SPEC_410 && host->v4_mode &&
+ (use_cmd12 || use_cmd23)) {
*mode |= SDHCI_TRNS_AUTO_SEL;
ctrl2 = sdhci_readw(host, SDHCI_HOST_CONTROL2);
--
2.28.0
