Hi Rafael
On Sun, 4 Mar 2012, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@xxxxxxx>
>
> A runtime suspend of an MMC controller belonging to a power domain
> or, in a more complicated scenario, a runtime suspend of another
> device in the same power domain, may cause power to be removed from
> the entire domain. In that case, the amount of time necessary to
> runtime-resume the MMC controller is often substantially greater
> than the time needed to enable its clock. That may hurt performance
> in some situations, because user data may need to wait for the
> controller to become operational, so we should make it possible to
> prevent that from happening.
>
> For this reason, introduce a new sysfs attribute for MMC hosts,
> pm_latency_limit_ms, allowing user space to specify the upper bound
> of the time necessary to bring the (runtime-suspended) host up after
> the resume of it has been requested. However, make that attribute
> appear ony for the hosts whose drivers declare support for PM QoS by
> populating the pm_qos member of struct mmc_host before registering
> the host.
>
> Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> ---
> Documentation/mmc/mmc-dev-attrs.txt | 24 ++++++++++++
> drivers/mmc/core/host.c | 67 ++++++++++++++++++++++++++++++++++++
> include/linux/mmc/host.h | 9 ++++
> 3 files changed, 100 insertions(+)
>
> Index: linux/drivers/mmc/core/host.c
> ===================================================================
> --- linux.orig/drivers/mmc/core/host.c
> +++ linux/drivers/mmc/core/host.c
> @@ -293,6 +293,68 @@ static inline void mmc_host_clk_sysfs_in
>
> #endif
>
> +static ssize_t pm_qos_val_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct mmc_host *host = cls_dev_to_mmc_host(dev);
> + return snprintf(buf, PAGE_SIZE, "%d\n", host->pm_qos->val);
> +}
> +
> +static ssize_t pm_qos_val_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t count)
> +{
> + struct mmc_host *host = cls_dev_to_mmc_host(dev);
> + s32 value;
> + int ret;
> +
> + if (kstrtos32(buf, 0, &value))
> + return -EINVAL;
> +
> + if (value < 0)
> + return -EINVAL;
> +
> + host->pm_qos->val = value;
> + ret = dev_pm_qos_update_request(&host->pm_qos->req, value);
This seems strange, is this really needed? First assign the new value to
the request, and then pass it to dev_pm_qos_update_request() with the
request and as a separate parameter additionally?
Further, isn't value, used in dev_pm_qos*() calls in microseconds, whereas
your patch is supposed to operate in miliseconds?
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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