lkml.org 
[lkml]   [2020]   [Oct]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v2] mmc: sdhci-acpi: AMDI0040: Allow changing HS200/HS400 driver strength
    From
    Date
    On 27/10/20 10:46 am, Victor Ding wrote:
    > From: Raul E Rangel <rrangel@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 <rrangel@chromium.org>
    > Signed-off-by: Victor Ding <victording@google.com>

    Apart from unnecessary blank line after "return preset_driver_strength;"

    Acked-by: Adrian Hunter <adrian.hunter@intel.com>

    >
    > ---
    >
    > Changes in v2:
    > By Victor Ding <victording@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)
    >

    \
     
     \ /
      Last update: 2020-10-27 14:03    [W:3.259 / U:0.244 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site