On Mon, 4 Feb 2019 at 10:58, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > > On 1/02/19 10:10 AM, Ulf Hansson wrote: > > 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. > > The switch from HS400 mode is done for tuning at times when CRC errors are a > possibility e.g. after a CRC error during transfer. So if the frequency is > not to be reduced, then some mitigation is needed for the possibility that > the CMD6 response itself will have a CRC error. That's a good point! However, how can we know that a CMD6 command is successfully completed, if there is CRC errors detected during the transmission? I guess we can't!? Kind regards Uffe
