Re: [PATCH 1/2] mmc: jz4740: Don't change parent clock rate for some SoCs

[Paul Cercueil]

Le ven. 18 nov. 2022 à 13:04:30 +0000, Paul Cercueil 
<paul@xxxxxxxxxxxxxxx> a écrit :
> Hi Siarhei,
>
> Le ven. 18 nov. 2022 à 12:51:54 +0300, Siarhei Volkau 
> <lis8215@xxxxxxxxx> a écrit :
> > пт, 18 нояб. 2022 г. в 12:27, Paul Cercueil 
> > <paul@xxxxxxxxxxxxxxx>:
> > >  Hi,
> > >
> > >  (Ingenic SoCs maintainer here)
> > >
> > >  Le ven. 18 nov. 2022 à 09:45:48 +0100, Ulf Hansson
> > >  <ulf.hansson@xxxxxxxxxx> a écrit :
> > >  > On Tue, 8 Nov 2022 at 05:53, Siarhei Volkau <lis8215@xxxxxxxxx> 
> > > wrote:
> > >  >>
> > >  >>  Some SoCs have one clock divider for all MMC units, thus 
> > > changing
> > >  >> one
> > >  >>  affects others as well. This leads to random hangs and memory
> > >  >>  corruptions, observed on the JZ4755 based device with two MMC 
> > > slots
> > >  >>  used at the same time.
> > >  >
> > >  > Urgh, that sounds like broken HW to me.
> > >  >
> > >  > The MMC blocks could share a parent clock (that would need a 
> > > fixed
> > >  > rate for it to be applied), assuming there is a separate 
> > > gate/divider
> > >  > available per block. But there isn't'?
> > >
> > >  They do share a parent clock and have separate gates, and each MMC 
> > > IP
> > >  block has an internal divider for the bus frequency derived from 
> > > that
> > >  shared clock.
> > >
> > >  >>
> > >  >>  List of SoCs affected includes: JZ4725b, JZ4755, JZ4760 and 
> > > JZ4760b.
> > >  >>  However, the MMC driver doesn't distinguish JZ4760 and JZ4770
> > >  >>  which shall remain its behavior. For the JZ4755 is sufficient 
> > > to
> > >  >>  use JZ4725b's binding. JZ4750 is outside of the patch.
> > >  >>
> > >  >>  The MMC core has its own clock divisor, rather coarse but 
> > > suitable
> > >  >> well,
> > >  >>  and it shall keep the role of tuning clock for the MMC host in 
> > > that
> > >  >>  case.
> > >  >
> > >  > The mmc core doesn't have a clock divisor, but it does control 
> > > the bus
> > >  > clock frequency through the ->set_ios() host ops. It needs to do 
> > > that,
> > >  > to be able to conform to the (e)MMC, SD and SDIO specifications.
> > >  >
> > >  > Can you please try to elaborate on the above, so I can better
> > >  > understand your point?
> > >
> > >  Yes, I don't really understand the patch, TBH.
> > >
> > >  The "clk_set_rate" call will only set the shared clock to the 
> > > *maximum*
> > >  clock frequency (host->mmc->f_max) which should be the exact same
> > >  across all MMC IPs.
> >
> > That's the case I need different "f_max" for my HW, for some reason
> > internal slot can't do a full rate (48MHz) but the external can, the 
> > same
> > card used for checking. So I want to set 24M for mmc0, and 48M for 
> > mmc1
> > with respect to hardware limitation.
>
> The JZ4760B programming manual states that the controller is "fully 
> compatible with the SD Memory Card Specification 2.0". In that 
> specification, the bus speed is max. 25 MHz.
>
> The programming manual also says: "In data transfer mode, the MSC 
> controller can operate card with clock rate fpp (0 ~ 25Mhz)."
>
> So the max-frequency really should be 25 MHz.

Nevermind. I read wrong, at least the SD spec. (the quote of the 
programming manual is still concerning though).

It's rated for 25 MB/s, so 50 MHz on 4 lanes.

Cheers,
-Paul

> > >  So it doesn't matter if it's set 3 times by 3 different instances 
> > > of
> > >  the IP, as long as they all request the same value.
> > >
> > >  Besides, I know for a fact that the mainline driver works fine on 
> > > the
> > >  JZ4760(B) and JZ4725B.
> > >
> > >  Finally... even if it was correct, this change would break
> > >  compatibility with old Device Tree files.
> > >
> > >  Cheers,
> > >  -Paul
> > >
> > >  >>
> > >  >>  Signed-off-by: Siarhei Volkau <lis8215@xxxxxxxxx>
> > >  >
> > >  > Kind regards
> > >  > Uffe
> > >  >
> > >  >>  ---
> > >  >>   drivers/mmc/host/jz4740_mmc.c | 10 +++++++++-
> > >  >>   1 file changed, 9 insertions(+), 1 deletion(-)
> > >  >>
> > >  >>  diff --git a/drivers/mmc/host/jz4740_mmc.c
> > >  >> b/drivers/mmc/host/jz4740_mmc.c
> > >  >>  index dc2db9c18..d390ff31d 100644
> > >  >>  --- a/drivers/mmc/host/jz4740_mmc.c
> > >  >>  +++ b/drivers/mmc/host/jz4740_mmc.c
> > >  >>  @@ -114,6 +114,7 @@ enum jz4740_mmc_version {
> > >  >>          JZ_MMC_JZ4740,
> > >  >>          JZ_MMC_JZ4725B,
> > >  >>          JZ_MMC_JZ4760,
> > >  >>  +       JZ_MMC_JZ4770,
> > >  >>          JZ_MMC_JZ4780,
> > >  >>          JZ_MMC_X1000,
> > >  >>   };
> > >  >>  @@ -887,7 +888,13 @@ static int 
> > > jz4740_mmc_set_clock_rate(struct
> > >  >> jz4740_mmc_host *host, int rate)
> > >  >>          int real_rate;
> > >  >>
> > >  >>          jz4740_mmc_clock_disable(host);
> > >  >>  -       clk_set_rate(host->clk, host->mmc->f_max);
> > >  >>  +
> > >  >>  +       /*
> > >  >>  +        * Changing rate on these SoCs affects other MMC units 
> > > too.
> > >  >>  +        * Make sure the rate is configured properly by the CGU
> > >  >> driver.
> > >  >>  +        */
> > >  >>  +       if (host->version != JZ_MMC_JZ4725B && host->version !=
> > >  >> JZ_MMC_JZ4760)
> > >  >>  +               clk_set_rate(host->clk, host->mmc->f_max);
> > >  >>
> > >  >>          real_rate = clk_get_rate(host->clk);
> > >  >>
> > >  >>  @@ -992,6 +999,7 @@ static const struct of_device_id
> > >  >> jz4740_mmc_of_match[] = {
> > >  >>          { .compatible = "ingenic,jz4740-mmc", .data = (void *)
> > >  >> JZ_MMC_JZ4740 },
> > >  >>          { .compatible = "ingenic,jz4725b-mmc", .data = (void
> > >  >> *)JZ_MMC_JZ4725B },
> > >  >>          { .compatible = "ingenic,jz4760-mmc", .data = (void *)
> > >  >> JZ_MMC_JZ4760 },
> > >  >>  +       { .compatible = "ingenic,jz4770-mmc", .data = (void *)
> > >  >> JZ_MMC_JZ4770 },
> > >  >>          { .compatible = "ingenic,jz4775-mmc", .data = (void *)
> > >  >> JZ_MMC_JZ4780 },
> > >  >>          { .compatible = "ingenic,jz4780-mmc", .data = (void *)
> > >  >> JZ_MMC_JZ4780 },
> > >  >>          { .compatible = "ingenic,x1000-mmc", .data = (void *)
> > >  >> JZ_MMC_X1000 },
> > >  >>  --
> > >  >>  2.36.1
> > >  >>