linux-kernel - Re: [RFC PATCH] async: Add cmdline option to specify drivers to be async probed

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Date:   Fri, 25 Jan 2019 11:22:49 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Feng Tang <feng.tang@...el.com>, alexander.h.duyck@...ux.intel.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] async: Add cmdline option to specify drivers to be
 async probed

On Fri, Jan 25, 2019 at 5:20 AM Feng Tang <feng.tang@...el.com> wrote:
>
> Asynchronous driver probing can help much on kerenl fastboot, and
> this option can provide a flexible way to optimize and quickly verify
> async driver probe.
>
> Also it will help in below cases:
> * Some driver actually covers several family of HWs, some of which
>   could use async probling while others don't. So we can't simply
>   turn on the PROBE_PREFER_ASYNCHRONOUS flag in driver, but use this
>   cmdline option, like igb driver discussed at
>   https://www.spinics.net/lists/netdev/msg545986.html
>
> * For SOC (System on Chip) with multiple spi or i2c controllers, most
>   of the slave spi/i2c devices will be assigned with fixed controller
>   number, which prevents these spi/i2c controller drivers to be async
>   probed. For plaforms not using these spi/i2c slave devices, they can
>   use this cmdline option to benefit from the async probing.
>
> Suggested-by: Alexander Duyck <alexander.duyck@...il.com>

Actually instead of using my personal email I would prefer if you used
"alexander.h.duyck@...ux.intel.com".

> Signed-off-by: Feng Tang <feng.tang@...el.com>
> ---
>  drivers/base/dd.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 8ac10af..1f257561 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -57,6 +57,10 @@ static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
>  static struct dentry *deferred_devices;
>  static bool initcalls_done;
>
> +/* Save the async probe drivers' name from kernel cmdline */
> +#define ASYNC_DRV_NAMES_MAX_LEN        256
> +static char async_probe_drv_names[ASYNC_DRV_NAMES_MAX_LEN];
> +
>  /*
>   * In some cases, like suspend to RAM or hibernation, It might be reasonable
>   * to prohibit probing of devices as it could be unsafe.
> @@ -674,8 +678,26 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
>         return ret;
>  }
>
> +static inline bool cmdline_requested_async_probing(const char *drv_name)
> +{
> +       return parse_option_str(async_probe_drv_names, drv_name);
> +}
> +
> +static int __init save_async_options(char *buf)
> +{
> +       if (strlen(buf) >= ASYNC_DRV_NAMES_MAX_LEN)
> +               printk(KERN_WARNING "Too long list for async_probe_drv_names!");
> +
> +       strlcpy(async_probe_drv_names, buf, ASYNC_DRV_NAMES_MAX_LEN - 1);
> +       return 0;
> +}
> +__setup("driver_async_probe=", save_async_options);
> +
>  bool driver_allows_async_probing(struct device_driver *drv)
>  {
> +       if (unlikely(cmdline_requested_async_probing(drv->name)))
> +               return true;
> +

Instead of placing it here it might make more sense to place it down
in the "default" case. This way we don't override a
PROBE_FORCE_SYNCHRONOUS if that is the probe type value used by the
driver.

>         switch (drv->probe_type) {
>         case PROBE_PREFER_ASYNCHRONOUS:
>                 return true;
> --
> 2.7.4
>