Re: [alsa-devel] [PATCH 2/2] V4 regmap: Apply optional delay in multi_reg_write/register_patch

[Takashi Iwai <tiwai@suse.de>]

On Tue, 14 Jul 2015 16:45:52 +0200,
Nariman Poushin wrote:
> 
> We treat a delay in a sequence the same way we treat a page change as
> they are logically similar in that you can coalesce all write before
> a delay (in the same way you can coalesce all writes before a page
> change is needed)
> 
> Signed-off-by: Nariman Poushin <nariman@opensource.wolfsonmicro.com>
> ---
>  drivers/base/regmap/regmap.c | 65 ++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 59 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
> index 0a849ee..a67473c2 100644
> --- a/drivers/base/regmap/regmap.c
> +++ b/drivers/base/regmap/regmap.c
> @@ -18,6 +18,7 @@
>  #include <linux/of.h>
>  #include <linux/rbtree.h>
>  #include <linux/sched.h>
> +#include <linux/delay.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include "trace.h"
> @@ -47,6 +48,17 @@ static int _regmap_bus_reg_write(void *context, unsigned int reg,
>  static int _regmap_bus_raw_write(void *context, unsigned int reg,
>  				 unsigned int val);
>  
> +static void regmap_sequence_delay(unsigned int delay_us)
> +{
> +	/* For small delays it isn't worth setting up the hrtimers
> +	 * so fall back on udelay
> +	 */
> +	if (delay_us < 10)
> +		udelay(delay_us);
> +	else
> +		usleep_range(delay_us, delay_us * 2);
> +}

I think usleep_range() can't be used for fast_io, which is performed
inside a spinlock.  And, the locking can't be known explicitly,
e.g. the caller may set its own config->lock, so even the check for
fast_io isn't enough.


Takashi