linux-kernel - [PATCH 1/2] mmc: core: adjust polling interval for CMD1

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Message-Id: <20211022063920.2145-1-huijin.park@samsung.com>
Date:   Fri, 22 Oct 2021 15:39:19 +0900
From:   Huijin Park <huijin.park@...sung.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Huijin Park <bbanghj.park@...il.com>,
        Huijin Park <huijin.park@...sung.com>
Subject: [PATCH 1/2] mmc: core: adjust polling interval for CMD1

In mmc_send_op_cond(), loops are continuously performed at the same
interval of 10 ms.  However the behaviour is not good for some eMMC
which can be out from a busy state earlier than 10 ms if normal.

Therefore, this patch adjusts the waiting interval time. The interval
time starts at 1 ms, but doubles until the range reaches 10 ms for
each loop.

The reason for adjusting the interval time is that it is important
to reduce the eMMC initialization time, especially in devices that
use eMMC as rootfs.

Test log(eMMC:KLM8G1GETF-B041):

before: 12 ms (0.439407 - 0.427186)
[0.419407] mmc0: starting CMD0 arg 00000000 flags 000000c0
[0.422652] mmc0: starting CMD1 arg 00000000 flags 000000e1
[0.424270] mmc0: starting CMD0 arg 00000000 flags 000000c0
[0.427186] mmc0: starting CMD1 arg 40000080 flags 000000e1<-start
[0.439407] mmc0: starting CMD1 arg 40000080 flags 000000e1<-finish
[0.439721] mmc0: starting CMD2 arg 00000000 flags 00000007

after: 4 ms (0.431725 - 0.427352)
[0.419575] mmc0: starting CMD0 arg 00000000 flags 000000c0
[0.422819] mmc0: starting CMD1 arg 00000000 flags 000000e1
[0.424435] mmc0: starting CMD0 arg 00000000 flags 000000c0
[0.427352] mmc0: starting CMD1 arg 40000080 flags 000000e1<-start
[0.428913] mmc0: starting CMD1 arg 40000080 flags 000000e1
[0.431725] mmc0: starting CMD1 arg 40000080 flags 000000e1<-finish
[0.432038] mmc0: starting CMD2 arg 00000000 flags 00000007

Signed-off-by: Huijin Park <huijin.park@...sung.com>

diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index 0c54858e89c0..61b4ffdc89ce 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -177,6 +177,7 @@ int mmc_send_op_cond(struct mmc_host *host, u32 ocr, u32 *rocr)
 {
 	struct mmc_command cmd = {};
 	int i, err = 0;
+	int interval = 1, interval_max = 10;
 
 	cmd.opcode = MMC_SEND_OP_COND;
 	cmd.arg = mmc_host_is_spi(host) ? 0 : ocr;
@@ -198,7 +199,9 @@ int mmc_send_op_cond(struct mmc_host *host, u32 ocr, u32 *rocr)
 
 		err = -ETIMEDOUT;
 
-		mmc_delay(10);
+		mmc_delay(interval);
+		if (interval < interval_max)
+			interval = min(interval * 2, interval_max);
 
 		/*
 		 * According to eMMC specification v5.1 section 6.4.3, we
-- 
2.17.1