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 <[email protected]> Reviewed-by: Grant Grundler <[email protected]> Reviewed-by: Doug Anderson <[email protected]> --- drivers/mmc/host/sdhci.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c index df6d85a..05ffac2 100644 --- a/drivers/mmc/host/sdhci.c +++ b/drivers/mmc/host/sdhci.c @@ -1987,7 +1987,10 @@ static int sdhci_execute_tuning(struct mmc_host *mmc, u32 opcode) 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); /* -- 1.9.1.423.g4596e3a -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
