On Thu, 23 Jun 2022 at 10:00, Vincent Whitchurch
<vincent.whitchurch@xxxxxxxx> wrote:
>
> During board verification, there is a need to test the various supported
> eMMC/SD speed modes. However, since the framework chooses the best mode
> supported by the card and the host controller's caps, this currently
> necessitates changing the devicetree for every iteration.
>
> To make changing the modes easier, allow the various host controller
> capabilities to be cleared via a module parameter. (A per-controller
> debugfs wouldn't work since the controller needs to be re-probed to
> trigger re-init of cards. A module parameter is used instead of a
I think we could make use of a per-controller debugfs thing, if used
in combination with MMC_CAP_AGGRESSIVE_PM and runtime PM.
As runtime PM also has sysfs interface for each device, we can control
runtime PM for the card's device (to trigger re-initialization of the
card). In between runtime suspend/resume of the card's device, we
should be able to change the supported speed modes, through debug fs.
Would this work for you?
Kind regards
Uffe
> global debugfs to allow this to be also set via the kernel command
> line.)
>
> The values to be written are the raw MMC_CAP* values from
> include/linux/mmc/host.h. This is rather low-level, and these defines
> are not guaranteed to be stable, but it is perhaps good enough for the
> indented use case. A warning is emitted when the caps clearing is in
> effect.
>
> Example of use:
>
> # grep timing /sys/kernel/debug/mmc0/ios
> timing spec: 9 (mmc HS200)
>
> // MMC_CAP2_HS200_1_8V_SDR
> # echo $((1 << 5)) > /sys/module/mmc_core/parameters/caps2_clear
>
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/unbind
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/bind
> # grep timing /sys/kernel/debug/mmc0/ios
> timing spec: 8 (mmc DDR52)
>
> // MMC_CAP_1_8V_DDR
> # echo $((1 << 12)) > /sys/module/mmc_core/parameters/caps_clear
>
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/unbind
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/bind
> # grep timing /sys/kernel/debug/mmc0/ios
> timing spec: 1 (mmc high-speed)
>
> # echo 0 > /sys/module/mmc_core/parameters/caps2_clear
>
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/unbind
> # echo 16d40000.mmc > /sys/bus/platform/drivers/dwmmc_exynos/bind
> # grep timing /sys/kernel/debug/mmc0/ios
> timing spec: 9 (mmc HS200)
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
> ---
> drivers/mmc/core/host.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index 2ed2b4d5e5a5..37971b7c7f62 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -34,6 +34,10 @@
> #define cls_dev_to_mmc_host(d) container_of(d, struct mmc_host, class_dev)
>
> static DEFINE_IDA(mmc_host_ida);
> +static unsigned int caps_clear, caps2_clear;
> +
> +module_param(caps_clear, uint, 0644);
> +module_param(caps2_clear, uint, 0644);
>
> #ifdef CONFIG_PM_SLEEP
> static int mmc_host_class_prepare(struct device *dev)
> @@ -411,6 +415,14 @@ int mmc_of_parse(struct mmc_host *host)
> host->caps2 &= ~(MMC_CAP2_HS400_1_8V | MMC_CAP2_HS400_1_2V |
> MMC_CAP2_HS400_ES);
>
> + if (caps_clear || caps2_clear)
> + dev_warn(host->parent,
> + "clearing host controller caps %#x caps2 %#x\n",
> + caps_clear, caps2_clear);
> +
> + host->caps &= ~caps_clear;
> + host->caps2 &= ~caps2_clear;
> +
> /* Must be after "non-removable" check */
> if (device_property_read_u32(dev, "fixed-emmc-driver-type", &drv_type) == 0) {
> if (host->caps & MMC_CAP_NONREMOVABLE)
> --
> 2.34.1
>
