Re: [PATCH v2] mmc: sdhci-acpi: AMDI0040: Allow changing HS200/HS400 driver strength

[Raul Rangel]

Thanks Victor and Ulf!

On Tue, Oct 27, 2020 at 7:42 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Tue, 27 Oct 2020 at 09:46, Victor Ding <victording@xxxxxxxxxx> wrote:
> >
> > From: Raul E Rangel <rrangel@xxxxxxxxxxxx>
> >
> > This change will allow platform designers better control over signal
> > integrity by allowing them to tune the HS200 and HS400 driver strengths.
> >
> > The driver strength was previously hard coded to A to solve boot
> > problems with certain platforms. This driver strength does not
> > universally apply to all platforms so we need a knob to adjust it.
> >
> > All older platforms currently have the SDR104 preset hard coded to A in
> > the firmware. This means that switching from the hard coded value in
> > the kernel to reading the SDR104 preset is a no-op for these platforms.
> > Newer platforms will have properly set presets. So this change will
> > support both new and old platforms.
> >
> > Signed-off-by: Raul E Rangel <rrangel@xxxxxxxxxxxx>
> > Signed-off-by: Victor Ding <victording@xxxxxxxxxx>
>
> Applied for next, thanks!
>
> Note that I amended the patch to fix the white-space issue, as pointed
> out by Adrian.
>
> Kind regards
> Uffe
>
>
> >
> > ---
> >
> > Changes in v2:
> > By Victor Ding <victording@xxxxxxxxxx>
> >  - Rebased the patch by using FIELD_GET for preset value bit masks.
> >  - (No functional changes).
> >
> > The original patch was developed by Raul E Rangel.
> > https://patchwork.kernel.org/project/linux-mmc/patch/20200928154718.2.Ic6b6031366f090393d00a53fd69e1ada31ceb29e@changeid/
> >
> >  drivers/mmc/host/sdhci-acpi.c | 39 ++++++++++++++++++++++++++++++++---
> >  1 file changed, 36 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-acpi.c b/drivers/mmc/host/sdhci-acpi.c
> > index 54205e3be9e8..225cb34cf1b9 100644
> > --- a/drivers/mmc/host/sdhci-acpi.c
> > +++ b/drivers/mmc/host/sdhci-acpi.c
> > @@ -5,6 +5,7 @@
> >   * Copyright (c) 2012, Intel Corporation.
> >   */
> >
> > +#include <linux/bitfield.h>
> >  #include <linux/init.h>
> >  #include <linux/export.h>
> >  #include <linux/module.h>
> > @@ -545,10 +546,42 @@ struct amd_sdhci_host {
> >
> >  static int amd_select_drive_strength(struct mmc_card *card,
> >                                      unsigned int max_dtr, int host_drv,
> > -                                    int card_drv, int *drv_type)
> > +                                    int card_drv, int *host_driver_strength)
> >  {
> > -       *drv_type = MMC_SET_DRIVER_TYPE_A;
> > -       return MMC_SET_DRIVER_TYPE_A;
> > +       struct sdhci_host *host = mmc_priv(card->host);
> > +       u16 preset, preset_driver_strength;
> > +
> > +       /*
> > +        * This method is only called by mmc_select_hs200 so we only need to
> > +        * read from the HS200 (SDR104) preset register.
> > +        *
> > +        * Firmware that has "invalid/default" presets return a driver strength
> > +        * of A. This matches the previously hard coded value.
> > +        */
> > +       preset = sdhci_readw(host, SDHCI_PRESET_FOR_SDR104);
> > +       preset_driver_strength = FIELD_GET(SDHCI_PRESET_DRV_MASK, preset);
> > +
> > +       /*
> > +        * We want the controller driver strength to match the card's driver
> > +        * strength so they have similar rise/fall times.
> > +        *
> > +        * The controller driver strength set by this method is sticky for all
> > +        * timings after this method is called. This unfortunately means that
> > +        * while HS400 tuning is in progress we end up with mismatched driver
> > +        * strengths between the controller and the card. HS400 tuning requires
> > +        * switching from HS400->DDR52->HS->HS200->HS400. So the driver mismatch
> > +        * happens while in DDR52 and HS modes. This has not been observed to
> > +        * cause problems. Enabling presets would fix this issue.
> > +        */
> > +       *host_driver_strength = preset_driver_strength;
> > +
> > +       /*
> > +        * The resulting card driver strength is only set when switching the
> > +        * card's timing to HS200 or HS400. The card will use the default driver
> > +        * strength (B) for any other mode.
> > +        */
> > +       return preset_driver_strength;
> > +
> >  }
> >
> >  static void sdhci_acpi_amd_hs400_dll(struct sdhci_host *host, bool enable)
> > --
> > 2.29.0.rc2.309.g374f81d7ae-goog
> >