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?
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>
thanks,
drew
