[PATCH RFC 4/4] mmc: sdhci-of-dwcmshc: Add support for T-Head TH1520

[Drew Fustini]

On Tue, Jul 25, 2023 at 11:03:44PM +0800, Jisheng Zhang wrote:
> On Mon, Jul 24, 2023 at 05:59:18PM -0700, Drew Fustini wrote:
> > Add basic support for the T-Head TH1520 SoC mmc controller. The new
> > compatible "thead,th1520-dwcmshc" enables basic support by:
> 
> Hi Drew,
> 
> > 
> >  - Enabling v4 mode to properly communicate with the mmc device
> >  - Setting quirk to disable ADMA
> >  - Setting flag to disable SDMA and force PIO mode
> >  - Turing .reset op into a no-op as the driver does not yet know how to
> >    configure the phy. Rely on the vendor u-boot to have configured the
> >    phy and do not reset the controller in Linux.
> 
> The last three itmes are not acceptable. The controller supports ADMA
> well, can you plz bring in the phy driver? We can't rely on bootloader to
> configure phy.

Yes, that makes sense that this is not acceptable. The T-Head vendor
kernel seems to contain all the necessary information needed to add the
phy configuration to sdhci-of-dwcmshc.

The shipping kernel for the BeagleV Ahead [1] is based on the T-Head SDK
releases. I looked at changes to drivers/mmc and found that key changes
are from Linux_SDK_V0.9.5 [2] and Linux_SDK_V1.0.2 [3].

That kernel contains drivers/mmc/host/sdhci-of-dwcmshc.h [4] which seems
to define information about the phy registers. The version of
drivers/mmc/host/sdhci-of-dwcmshc.h in that kernel defines several
functions for the phy config and controller reset:

sdhci_phy_1_8v_init_no_pull
sdhci_phy_3_3v_init_no_pull
snps_phy_1_8v_init
snps_phy_3_3v_init
snps_sdhci_set_phy
snps_sdhci_reset

I'll look into adapting that code into the upstream sdhci-of-dwcmshc.

Thanks,
Drew

[1] https://git.beagleboard.org/beaglev-ahead/beaglev-ahead-linux
[2] https://gist.github.com/pdp7/8d85d736dea24957c017eefdeb882668
[3] https://gist.github.com/pdp7/c1d3a18f9b7c25e630573d5953a58c99
[4] https://git.beagleboard.org/beaglev-ahead/beaglev-ahead-linux/-/blob/beaglev-v5.10.113-1.1.2/drivers/mmc/host/sdhci-of-dwcmshc.h
[5] https://git.beagleboard.org/beaglev-ahead/beaglev-ahead-linux/-/blob/beaglev-v5.10.113-1.1.2/drivers/mmc/host/sdhci-of-dwcmshc.c