On 27/10/20 10:46 am, Victor Ding wrote: > From: Raul E Rangel <rran...@chromium.org> > > 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 <rran...@chromium.org> > Signed-off-by: Victor Ding <victord...@google.com>
Apart from unnecessary blank line after "return preset_driver_strength;" Acked-by: Adrian Hunter <adrian.hun...@intel.com> > > --- > > Changes in v2: > By Victor Ding <victord...@google.com> > - 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; > + Unnecessary blank line. > } > > static void sdhci_acpi_amd_hs400_dll(struct sdhci_host *host, bool enable) >
