Re: [PATCH v8 4/4] riscv: dts: thead: Enable LicheePi 4A eMMC and microSD

[Xi Ruoyao]

On Sat, 2024-03-23 at 18:25 -0700, Drew Fustini wrote:
> On Wed, Mar 20, 2024 at 03:28:19PM +0300, Maxim Kiselev wrote:
> > Hi Xi, Drew
> > 
> > I have the same problem with SD on my LicheePi 4A.
> > 
> > After some investigations I found how to fix this tuning error.
> > Here is the patch that increases tuning loop count from
> > 40(MAX_TUNING_LOOP at sdhci.c) to 128.
> > 
> > diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c
> > b/drivers/mmc/host/sdhci-of-dwcmshc.c
> > index 8d6cfb648096..da8f5820fb69 100644
> > --- a/drivers/mmc/host/sdhci-of-dwcmshc.c
> > +++ b/drivers/mmc/host/sdhci-of-dwcmshc.c
> > @@ -706,6 +706,7 @@ static int th1520_execute_tuning(struct
> > sdhci_host
> > *host, u32 opcode)
> > 
> >         /* perform tuning */
> >         sdhci_start_tuning(host);
> > +       host->tuning_loop_count = 128:
> >         host->tuning_err = __sdhci_execute_tuning(host, opcode);
> >         if (host->tuning_err) {
> >                 /* disable auto-tuning upon tuning error */
> > 
> > After that change tuning works fine. The same value of loop count is
> > used in RevyOS BSP
> > https://github.com/revyos/thead-kernel/blob/c6d4e5df18a17903d012ffd89e67d0ee5ce6cf2d/drivers/mmc/host/sdhci-of-dwcmshc.c#L185
> > 
> > Honestly, it looks a little bit strange for me.
> > 
> > It seems that the tuning algorithm requires to move through
> > all the taps of delay line(128 taps?) even if we use THRESHOLD_MODE
> > instend LARGEST_WIN_MODE (I mean bit 2 in AT_CTRL_R(0x540)
> > register).
> > 
> > Xi, could you also test my fix on your board?

It works for me as well.  I'm now getting:

[    0.854357] mmc1: new ultra high speed SDR104 SDXC card at address aaaa
[    0.862267] mmcblk1: mmc1:aaaa SR256 238 GiB
[    0.876623]  mmcblk1: p1

Tested-by: Xi Ruoyao <xry111@xxxxxxxxxxx>

Thanks a lot!

> Thanks for figuring this out!
> 
> When I was upstreaming support, I noticed __sdhci_execute_tuning() in
> T-Head's version of sdhci-of-dwcmshc.c seemed to duplicate what already
> existed in drivers/mmc/host/sdhci.c. I had thought T-Head copied it
> because it was a static function.
> 
> 9cc811a342be ("mmc: sdhci: add __sdhci_execute_tuning() to header")
> allowed me to remove __sdhci_execute_tuning() from sdhci-of-dwcmshc.
> However, I overlooked this resulted in changing the tuning loop from
> 128 back to the upstream default of 40.
> 
> Before this change, the microSD did work for me on the lpi4 but I would
> see the following:
> 
> [    4.182483] mmc1: Tuning failed, falling back to fixed sampling
> clock
> [    4.189022] sdhci-dwcmshc ffe7090000.mmc: tuning failed: -11
> [    4.194734] mmc1: tuning execution failed: -5
> [    4.287899] mmc1: new high speed SDHC card at address aaaa
> [    4.299763] mmcblk1: mmc1:aaaa SD32G 29.7 GiB
> [    4.316963]  mmcblk1: p1 p2
> 
> root@lpi4amain:~# cat /sys/kernel/debug/mmc1/ios
> clock:		50000000 Hz
> actual clock:	49500000 Hz
> vdd:		21 (3.3 ~ 3.4 V)
> bus mode:	2 (push-pull)
> chip select:	0 (don't care)
> power mode:	2 (on)
> bus width:	2 (4 bits)
> timing spec:	2 (sd high-speed)
> signal voltage:	0 (3.30 V)
> driver type:	0 (driver type B)
> 
> With the change to 128, I no longer see the tuning failure and the
> microSD continues to work okay:
> 
> [    4.307040] mmc1: new ultra high speed SDR104 SDHC card at address
> aaaa
> [    4.320462] mmcblk1: mmc1:aaaa SD32G 29.7 GiB
> [    4.338646]  mmcblk1: p1 p2
> 
> root@lpi4amain:/sys/kernel/debug/mmc1# cat ios
> clock:		198000000 Hz
> actual clock:	198000000 Hz
> vdd:		21 (3.3 ~ 3.4 V)
> bus mode:	2 (push-pull)
> chip select:	0 (don't care)
> power mode:	2 (on)
> bus width:	2 (4 bits)
> timing spec:	6 (sd uhs SDR104)
> signal voltage:	1 (1.80 V)
> driver type:	0 (driver type B)
> 
> This has the benefit of the card now works at 198 MHz in SDR104 mode
> instead of 50 MHz when tuning failed.
> 
> Tested-by: Drew Fustini <drew@xxxxxxxx>

-- 
Xi Ruoyao <xry111@xxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University