[PATCH] clocksource: dw_apb_timer_of: support timer-based delay

[Jisheng Zhang]

Dear Daniel,

On Fri, 30 Oct 2015 16:27:39 +0800
Jisheng Zhang <jszhang at marvell.com> wrote:

> Implement an ARM delay timer to be used for udelay(). This allows us to
> skip the delay loop calibration at boot on Marvell BG2, BG2Q, BG2CD
> platforms. And after this patch, udelay() will be unaffected by CPU
> frequency changes.

The commit msg doesn't follow "clocksource/drivers/...: Dnnn.."
But I guess I'll need to post v2, v3 ..., I'll change the msg style in v2.

Thanks,
Jisheng

> 
> Signed-off-by: Jisheng Zhang <jszhang at marvell.com>
> ---
>  drivers/clocksource/Kconfig           | 10 ++++++++++
>  drivers/clocksource/dw_apb_timer_of.c | 16 ++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index a7726db..7b081805 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -29,6 +29,16 @@ config DW_APB_TIMER_OF
>  	select DW_APB_TIMER
>  	select CLKSRC_OF
>  
> +config DW_APB_TIMER_BASED_DELAY
> +	bool "DW APB timer based delay"
> +	depends on ARM && DW_APB_TIMER_OF
> +	default n
> +	help
> +	  This option enables support for using the DW APB timer to
> +	  implement timer-based delay. It is useful for skiping the
> +	  delay loop calibration at boot on some platforms. And the
> +	  udelay() will be unaffected by CPU frequency changes.
> +
>  config ROCKCHIP_TIMER
>  	bool
>  	select CLKSRC_OF
> diff --git a/drivers/clocksource/dw_apb_timer_of.c b/drivers/clocksource/dw_apb_timer_of.c
> index a19a3f6..4bab048 100644
> --- a/drivers/clocksource/dw_apb_timer_of.c
> +++ b/drivers/clocksource/dw_apb_timer_of.c
> @@ -16,6 +16,7 @@
>   * You should have received a copy of the GNU General Public License
>   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
> +#include <linux/delay.h>
>  #include <linux/dw_apb_timer.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> @@ -130,6 +131,17 @@ static void __init init_sched_clock(void)
>  	sched_clock_register(read_sched_clock, 32, sched_rate);
>  }
>  
> +#ifdef CONFIG_DW_APB_TIMER_BASED_DELAY
> +static unsigned long dw_apb_delay_timer_read(void)
> +{
> +	return ~readl_relaxed(sched_io_base);
> +}
> +
> +static struct delay_timer dw_apb_delay_timer = {
> +	.read_current_timer = dw_apb_delay_timer_read,
> +};
> +#endif
> +
>  static int num_called;
>  static void __init dw_apb_timer_init(struct device_node *timer)
>  {
> @@ -142,6 +154,10 @@ static void __init dw_apb_timer_init(struct device_node *timer)
>  		pr_debug("%s: found clocksource timer\n", __func__);
>  		add_clocksource(timer);
>  		init_sched_clock();
> +#ifdef CONFIG_DW_APB_TIMER_BASED_DELAY
> +		dw_apb_delay_timer.freq = sched_rate;
> +		register_current_timer_delay(&dw_apb_delay_timer);
> +#endif
>  		break;
>  	default:
>  		break;