Re: [PATCH] mmc: core: don't return 1 for max_discard

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On 12/19/13 10:01, Adrian Hunter wrote:
On 19/12/13 01:00, Stephen Warren wrote:
On 12/18/2013 03:27 PM, Stephen Warren wrote:
From: Stephen Warren<swarren@xxxxxxxxxx>

In mmc_do_calc_max_discard(), if only a single erase block can be
discarded within the host controller's timeout, don't allow discard
operations at all.

Previously, the code allowed sector-at-a-time discard (rather than
erase-block-at-a-time), which was chronically slow.

Without this patch, on the NVIDIA Tegra Cardhu board, the loops result
in qty == 1, which is immediately returned. This causes discard to
operate a single sector at a time, which is chronically slow. With this
patch in place, discard operates a single erase block at a time, which
is reasonably fast.

Alternatively, is the real fix a revert of e056a1b5b67b "mmc: queue: let
host controllers specify maximum discard timeout", followed by:

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 050eb262485c..35c5b5d86c99 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1950,7 +1950,6 @@ static int mmc_do_erase(struct mmc_card *card, unsigned int from,
         cmd.opcode = MMC_ERASE;
         cmd.arg = arg;
         cmd.flags = MMC_RSP_SPI_R1B | MMC_RSP_R1B | MMC_CMD_AC;
-       cmd.cmd_timeout_ms = mmc_erase_timeout(card, arg, qty);
         err = mmc_wait_for_cmd(card->host,&cmd, 0);
         if (err) {
                 pr_err("mmc_erase: erase error %d, status %#x\n",
@@ -1962,7 +1961,7 @@ static int mmc_do_erase(struct mmc_card *card, unsigned int from,
         if (mmc_host_is_spi(card->host))
                 goto out;

-       timeout = jiffies + msecs_to_jiffies(MMC_CORE_TIMEOUT_MS);
+       timeout = jiffies + msecs_to_jiffies(mmc_erase_timeout(card, arg, qty));
         do {
                 memset(&cmd, 0, sizeof(struct mmc_command));
                 cmd.opcode = MMC_SEND_STATUS;

That certainly also seems to solve the problem on my board...

But large erases will timeout when they should have been split into smaller
chunks.

A generic solution needs to be able to explain what happens when the host
controller *does* timeout.

Please correct me, but if Data Timeout Error is disabled, then this is not
an issue for most of the host controllers.

With best wishes,
Vladimir
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