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

[Adrian Hunter <adrian.hunter-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On 19/12/13 01:00, Stephen Warren wrote:
> On 12/18/2013 03:27 PM, Stephen Warren wrote:
>> From: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>
>> 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.