[PATCH v3] staging: dgnc: replace usleep_range with udelay

[PATCH v3] staging: dgnc: replace usleep_range with udelay

[Aishwarya Pant]

udelay is impelmented using a busy-wait loop and consumes CPU cycles
while usleep_range is implemented using interrupts.cls_flush_uart_write()
is called after a channel lock is acquired i.e. an atomic context.
Hence delay in this method should use udelay instead of usleep_range.

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>

---
Changes in v3:
	- Add a comment in code udelay to ignore checkpatch warning
Changes in v2:
	- Edit commit message to explain why udelay should be used

 drivers/staging/dgnc/dgnc_cls.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/dgnc/dgnc_cls.c b/drivers/staging/dgnc/dgnc_cls.c
index 28a3e16..ec190e5 100644
--- a/drivers/staging/dgnc/dgnc_cls.c
+++ b/drivers/staging/dgnc/dgnc_cls.c
@@ -609,7 +609,11 @@ static void cls_flush_uart_write(struct channel_t *ch)
 
 	writeb((UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_XMIT),
 	       &ch->ch_cls_uart->isr_fcr);
-	usleep_range(10, 20);
+
+	/* Ignore checkpatch warning to replace udelay by usleep_range
+	 * as this function is called under an atomic context
+	 */
+	udelay(10);
 
 	ch->ch_flags |= (CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
 }
-- 
2.7.4

Re: [Outreachy kernel] [PATCH v3] staging: dgnc: replace usleep_range with udelay

[Julia Lawall]

On Wed, 1 Mar 2017, Aishwarya Pant wrote:

> udelay is impelmented using a busy-wait loop and consumes CPU cycles
> while usleep_range is implemented using interrupts.cls_flush_uart_write()
> is called after a channel lock is acquired i.e. an atomic context.
> Hence delay in this method should use udelay instead of usleep_range.
>
> Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
>
> ---
> Changes in v3:
> 	- Add a comment in code udelay to ignore checkpatch warning
> Changes in v2:
> 	- Edit commit message to explain why udelay should be used
>
>  drivers/staging/dgnc/dgnc_cls.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/staging/dgnc/dgnc_cls.c b/drivers/staging/dgnc/dgnc_cls.c
> index 28a3e16..ec190e5 100644
> --- a/drivers/staging/dgnc/dgnc_cls.c
> +++ b/drivers/staging/dgnc/dgnc_cls.c
> @@ -609,7 +609,11 @@ static void cls_flush_uart_write(struct channel_t *ch)
>
>  	writeb((UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_XMIT),
>  	       &ch->ch_cls_uart->isr_fcr);
> -	usleep_range(10, 20);
> +
> +	/* Ignore checkpatch warning to replace udelay by usleep_range
> +	 * as this function is called under an atomic context
> +	 */
> +	udelay(10);

I think this doesn't follow the proper block comment format?

Anyway, perhaps something like "called in atomic context so usleep_range
not used" would be sufficient.

julia

>
>  	ch->ch_flags |= (CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
>  }
> --
> 2.7.4
>
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Re: [Outreachy kernel] [PATCH v3] staging: dgnc: replace usleep_range with udelay

[Aishwarya Pant]

On Wed, Mar 01, 2017 at 11:56:18AM +0100, Julia Lawall wrote:
> 
> 
> On Wed, 1 Mar 2017, Aishwarya Pant wrote:
> 
> > udelay is impelmented using a busy-wait loop and consumes CPU cycles
> > while usleep_range is implemented using interrupts.cls_flush_uart_write()
> > is called after a channel lock is acquired i.e. an atomic context.
> > Hence delay in this method should use udelay instead of usleep_range.
> >
> > Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
> >
> > ---
> > Changes in v3:
> > 	- Add a comment in code udelay to ignore checkpatch warning
> > Changes in v2:
> > 	- Edit commit message to explain why udelay should be used
> >
> >  drivers/staging/dgnc/dgnc_cls.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/dgnc/dgnc_cls.c b/drivers/staging/dgnc/dgnc_cls.c
> > index 28a3e16..ec190e5 100644
> > --- a/drivers/staging/dgnc/dgnc_cls.c
> > +++ b/drivers/staging/dgnc/dgnc_cls.c
> > @@ -609,7 +609,11 @@ static void cls_flush_uart_write(struct channel_t *ch)
> >
> >  	writeb((UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_XMIT),
> >  	       &ch->ch_cls_uart->isr_fcr);
> > -	usleep_range(10, 20);
> > +
> > +	/* Ignore checkpatch warning to replace udelay by usleep_range
> > +	 * as this function is called under an atomic context
> > +	 */
> > +	udelay(10);
> 
> I think this doesn't follow the proper block comment format?
>
 
I looked through the coding style docs and found the correct format 
for multi-line comments-
/*
 * Some comments spanning over
 * multiple lines
 */

What is convention for single line comments?

> Anyway, perhaps something like "called in atomic context so usleep_range
> not used" would be sufficient.
> 
> julia
> 
> >
> >  	ch->ch_flags |= (CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
> >  }
> > --
> > 2.7.4
> >
> > --
> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
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> > For more options, visit https://groups.google.com/d/optout.
> >

Re: [Outreachy kernel] [PATCH v3] staging: dgnc: replace usleep_range with udelay

[Julia Lawall]

On Wed, 1 Mar 2017, Aishwarya Pant wrote:

> On Wed, Mar 01, 2017 at 11:56:18AM +0100, Julia Lawall wrote:
> >
> >
> > On Wed, 1 Mar 2017, Aishwarya Pant wrote:
> >
> > > udelay is impelmented using a busy-wait loop and consumes CPU cycles
> > > while usleep_range is implemented using interrupts.cls_flush_uart_write()
> > > is called after a channel lock is acquired i.e. an atomic context.
> > > Hence delay in this method should use udelay instead of usleep_range.
> > >
> > > Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
> > >
> > > ---
> > > Changes in v3:
> > > 	- Add a comment in code udelay to ignore checkpatch warning
> > > Changes in v2:
> > > 	- Edit commit message to explain why udelay should be used
> > >
> > >  drivers/staging/dgnc/dgnc_cls.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/dgnc/dgnc_cls.c b/drivers/staging/dgnc/dgnc_cls.c
> > > index 28a3e16..ec190e5 100644
> > > --- a/drivers/staging/dgnc/dgnc_cls.c
> > > +++ b/drivers/staging/dgnc/dgnc_cls.c
> > > @@ -609,7 +609,11 @@ static void cls_flush_uart_write(struct channel_t *ch)
> > >
> > >  	writeb((UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_XMIT),
> > >  	       &ch->ch_cls_uart->isr_fcr);
> > > -	usleep_range(10, 20);
> > > +
> > > +	/* Ignore checkpatch warning to replace udelay by usleep_range
> > > +	 * as this function is called under an atomic context
> > > +	 */
> > > +	udelay(10);
> >
> > I think this doesn't follow the proper block comment format?
> >
>
> I looked through the coding style docs and found the correct format
> for multi-line comments-
> /*
>  * Some comments spanning over
>  * multiple lines
>  */
>
> What is convention for single line comments?

/* text */

julia

>
> > Anyway, perhaps something like "called in atomic context so usleep_range
> > not used" would be sufficient.
> >
> > julia
> >
> > >
> > >  	ch->ch_flags |= (CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
> > >  }
> > > --
> > > 2.7.4
> > >
> > > --
> > > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> > > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> > > To post to this group, send email to outreachy-kernel@googlegroups.com.
> > > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170301103315.GA4448%40aishwarya.
> > > For more options, visit https://groups.google.com/d/optout.
> > >
>