Re: [PATCH v2 2/3] mmc: core: API for temporarily disabling auto-retuning due to errors

From: Arend Van Spriel
Date: Wed Jun 05 2019 - 03:58:56 EST

On 6/3/2019 8:37 PM, Douglas Anderson wrote:
Normally when the MMC core sees an "-EILSEQ" error returned by a host
controller then it will trigger a retuning of the card. This is
generally a good idea.

However, if a command is expected to sometimes cause transfer errors
then these transfer errors shouldn't cause a re-tuning. This
re-tuning will be a needless waste of time. One example case where a
transfer is expected to cause errors is when transitioning between
idle (sometimes referred to as "sleep" in Broadcom code) and active
state on certain Broadcom WiFi cards. Specifically if the card was
already transitioning between states when the command was sent it
could cause an error on the SDIO bus.

Let's add an API that the SDIO card drivers can call that will
temporarily disable the auto-tuning functionality. Then we can add a
call to this in the Broadcom WiFi driver and any other driver that
might have similar needs.

NOTE: this makes the assumption that the card is already tuned well
enough that it's OK to disable the auto-retuning during one of these
error-prone situations. Presumably the driver code performing the
error-prone transfer knows how to recover / retry from errors. ...and
after we can get back to a state where transfers are no longer
error-prone then we can enable the auto-retuning again. If we truly
find ourselves in a case where the card needs to be retuned sometimes
to handle one of these error-prone transfers then we can always try a
few transfers first without auto-retuning and then re-try with
auto-retuning if the first few fail.

Without this change on rk3288-veyron-minnie I periodically see this in
the logs of a machine just sitting there idle:
dwmmc_rockchip ff0d0000.dwmmc: Successfully tuned phase to XYZ

Fixes: bd11e8bd03ca ("mmc: core: Flag re-tuning is needed on CRC errors")
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Note that are are a whole boatload of different ways that we could
provide an API for the Broadcom WiFi SDIO driver. This patch
illustrates one way but if maintainers feel strongly that this is too
ugly and have a better idea then I can give it a shot too. From a
purist point of view I kinda felt that the "expect errors" really
belonged as part of the mmc_request structure, but getting it into
there meant changing a whole pile of core SD/MMC APIs. Simply adding
it to the host seemed to match the current style better and was a less
intrusive change.

Hi Doug,

Sorry for bringing this up, but there used to be an issue with retuning in general, ie. the device handled tuning command 19 only once after startup. I guess that is no longer an issue given your results. I guess the problem goes away when you disable device sleep functionality. No what you want in terms of power consumption, but would be good to know. You can disable it with below patch.

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c b/drivers
index 15a40fd..18e90bd 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
@@ -307,7 +307,7 @@ struct rte_console {
#define BRCMF_IDLE_ACTIVE 0 /* Do not request any SD clock change
* when idle

#define KSO_WAIT_US 50