mmc: sdhci: remove mdelay in eMMC tuning
This patch removes an unneccesary 1ms mdelay in the HS200 tuning
loop, called 40 times per retuning. Currently this causes a latency
of >40ms on any emmc accesses triggering wake from runtime PM,
which can occur for a significant portion of reads on a mostly idle system.
The delay is left in place for SD Cards, which use
MMC_SEND_TUNING_BLOCK rather than MMC_SEND_TUNING_BLOCK_HS200.
I'm not able to find evidence that this is required for SD in the
specs I have access to, however this delay has been present from
initial checkin for SD so I have preserved the original behavior for
compatibility.
This has been verified to fix observed glitching on local audio
playback and recording on apps with inbuilt assumptions on storage
latency.
Signed-off-by: Nick Sanders <nsanders@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index a31f06d..255aaf1 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1994,7 +1994,10 @@
ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
tuning_loop_counter--;
timeout--;
- mdelay(1);
+
+ /* eMMC spec does not require a delay between tuning cycles */
+ if (opcode == MMC_SEND_TUNING_BLOCK)
+ mdelay(1);
} while (ctrl & SDHCI_CTRL_EXEC_TUNING);
/*