Commit 833b5117 authored May 28, 2018 by Martin Hicks Committed by Ulf Hansson May 29, 2018

mmc: Throttle calls to MMC_SEND_STATUS during mmc_do_erase()

This drastically reduces the rate at which the MMC_SEND_STATUS cmd polls
for completion of the MMC Erase operation. The patch does this by adding
a backoff sleep that starts by sleeping for short intervals (128-256us),
and ramps up to sleeping for 32-64ms.

Even on very quickly completing erase operations, the loop iterates a few
times, so not too much extra latency is added to these commands.

For long running discard operarations, like a full-device secure discard,
this change drops the interrupt rates on my single-core NXP I.MX6UL from
45000/s to about 20/s, and greatly improves system responsiveness.

Signed-off-by: Martin Hicks <mort@bork.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

parent a6720c02

drivers/mmc/core/core.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -1969,6 +1969,7 @@ static int mmc_do_erase(struct mmc_card *card, unsigned int from,
		unsigned int qty = 0, busy_timeout = 0;
		bool use_r1b_resp = false;
		unsigned long timeout;
		int loop_udelay=64, udelay_max=32768;
		int err;

		mmc_retune_hold(card->host);
		@@ -2093,9 +2094,15 @@ static int mmc_do_erase(struct mmc_card *card, unsigned int from,
		err = -EIO;
		goto out;
		}
		if ((cmd.resp[0] & R1_READY_FOR_DATA) &&
		R1_CURRENT_STATE(cmd.resp[0]) != R1_STATE_PRG)
		break;

		usleep_range(loop_udelay, loop_udelay*2);
		if (loop_udelay < udelay_max)
		loop_udelay *= 2;
		} while (1);

		} while (!(cmd.resp[0] & R1_READY_FOR_DATA) \|\|
		(R1_CURRENT_STATE(cmd.resp[0]) == R1_STATE_PRG));
		out:
		mmc_retune_release(card->host);
		return err;

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