On Fri, 1 Feb 2019 at 02:38, Chaotian Jing <chaotian.jing@xxxxxxxxxxxx> wrote: > > On Thu, 2019-01-31 at 16:58 +0100, Ulf Hansson wrote: > > On Thu, 31 Jan 2019 at 08:53, Chaotian Jing <chaotian.jing@xxxxxxxxxxxx> wrote: > > > > > > mmc_hs400_to_hs200() begins with the card and host in HS400 mode. > > > Therefore, any commands sent to the card should use HS400 timing. > > > It is incorrect to reduce frequency to 50Mhz before sending the switch > > > command, in this case, only reduce clock frequency to 50Mhz but without > > > host timming change, host is still in hs400 mode but clock changed from > > > 200Mhz to 50Mhz, which makes the tuning result unsuitable and cause > > > the switch command gets response CRC error. > > > > According the eMMC spec there is no violation by decreasing the clock > > frequency like this. We can use whatever value <=200MHz. > > > > However, perhaps in practice this becomes an issue, due to the tuning > > for HS400 has been done on the "current" frequency. > > > > As as start, I think you need to clarify this in the changelog. > > > Yes, reduce clock frequency to 50Mhz is no Spec violation, but it may > cause __mmc_switch() gets response CRC error, decreasing the clock but > without HOST mode change, on the host side, host driver do not know > what's operation the core layer want to do and can only set current bus > clock to 50Mhz, without tuning parameter change, it has a chance lead to > response CRC error. even lower clock frequency, but with the wrong > tuning parameter setting(the setting is of hs400 tuning @200Mhz). Right, makes sense. > > > > > > this patch refers to mmc_select_hs400(), make the reduce clock frequency > > > after card timing change. > > > > > > Signed-off-by: Chaotian Jing <chaotian.jing@xxxxxxxxxxxx> > > > --- > > > drivers/mmc/core/mmc.c | 8 ++++---- > > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c > > > index da892a5..21b811e 100644 > > > --- a/drivers/mmc/core/mmc.c > > > +++ b/drivers/mmc/core/mmc.c > > > @@ -1239,10 +1239,6 @@ int mmc_hs400_to_hs200(struct mmc_card *card) > > > int err; > > > u8 val; > > > > > > - /* Reduce frequency to HS */ > > > - max_dtr = card->ext_csd.hs_max_dtr; > > > - mmc_set_clock(host, max_dtr); > > > - > > > > As far as I can tell, the reason to why we change the clock frequency > > *before* the call to __mmc_switch() below, is probably to try to be on > > the safe side and conform to the spec. > > > Agree, it Must be more safe with lower clock frequency, but the > precondition is to make the host side recognize current timing is not > HS400 mode. it has no method to find a safe setting to ensure no > response CRC error when reduce clock from 200Mhz to 50Mhz. > > However, I think you have a point, as the call to __mmc_switch(), > > passes the "send_status" parameter as false, no other command than the > > CMD6 is sent to the card. > > > yes, the send status command was sent only after __mmc_switch() done. > > > /* Switch HS400 to HS DDR */ > > > val = EXT_CSD_TIMING_HS; > > > err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING, > > > @@ -1253,6 +1249,10 @@ int mmc_hs400_to_hs200(struct mmc_card *card) > > > > > > mmc_set_timing(host, MMC_TIMING_MMC_DDR52); > > > > > > + /* Reduce frequency to HS */ > > > + max_dtr = card->ext_csd.hs_max_dtr; > > > + mmc_set_clock(host, max_dtr); > > > + > > > > Perhaps it's even more correct to change the clock frequency before > > the call to mmc_set_timing(host, MMC_TIMING_MMC_DDR52). Otherwise you > > will be using the DDR52 timing in the controller, but with a too high > > frequency. > > > for Our host, it has no impact to change the clock before or after > change timing, as the mmc_set_timing() is only for host side, not > related to MMC card side and no commands sent do card before the > timing/clock change completed. Alright. After a second thought, it actually looks more consistent with mmc_select_hs400() to do it after, as what you propose in $subject patch. So, let's keep it as is. > > > err = mmc_switch_status(card); > > > if (err) > > > goto out_err; > > > -- > > > 1.8.1.1.dirty > > > > > > > Finally, it sounds like you are trying to fix a real problem, can you > > please provide some more information what is happening when the > > problem occurs at your side? > > > Yes, I got a problem with new kernel version. with > commit:57da0c042f4af52614f4bd1a148155a299ae5cd8, this commit makes > re-tuning every time when access RPMB partition. Okay, could you please add this as fixes tag for the next version of the patch. > > in fact, our host tuning result of hs400 is very stable and almost never > get response CRC error with clock frequency at 200Mhz. but cannot ensure > this tuning result also suitable when running at HS400 mode @50Mhz. as I > mentioned before, the host side does not know the reason of reduce clock > frequency to 50Mhz at HS400 mode, so what's the host side can do is only > reduce the bus clock to 50Mhz, even it can just only set the tuning > setting to default when clock frequency lower than 50Mhz, but both card > & host side are still at HS400 mode, still cannot ensure this setting is > suitable. Right, thanks for clarifying. So I am expecting a new version with a fixes tag and some clarification of the changelog, then I am ready to apply this to give it some test. Kind regards Uffe
