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

[Stephen Warren <swarren@wwwdotorg.org>]

On 12/19/2013 02:05 AM, Dong Aisheng wrote:
> On Thu, Dec 19, 2013 at 7:00 AM, Stephen Warren <swarren@wwwdotorg.org> wrote:
>> On 12/18/2013 03:27 PM, Stephen Warren wrote:
>>> From: Stephen Warren <swarren@nvidia.com>
>>>
>>> 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...
> 
> Is the change you mean here only include above 3 lines changes?
> If yes, it's strange to me how does this solve your issue?
> It actually does not change the max_discard_to/max_discard_bytes.
> It still discards only one sector one time if it does as before....

It's a revert of the patch which introduced max_discard_to, so all that
logic goes away completely, *then* the 3 lines above, which move the
timeout away from command submission (which is what I believe is
implemented by the controller's timeout HW) and to the CMD13 polling
operation (where we can implement whatever timeout we want, in the kernel).