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 > >
