[2/5] drivers: spi: core: Add optional stall delay between cs_change transfers
diff mbox series

Message ID 20190625131328.11883-2-alexandru.ardelean@analog.com
State New
Headers show
Series
  • [1/5] MAINTAINERS: add ADIS IMU driver library entry
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Commit Message

Alexandru Ardelean June 25, 2019, 1:13 p.m. UTC
Some devices like the ADIS16460 IMU require a stall period between
transfers, i.e. between when the CS is de-asserted and re-asserted. The
default value of 10us is not enough. This change makes the delay
configurable for when the next CS change goes active.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 drivers/spi/spi.c       | 3 ++-
 include/linux/spi/spi.h | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

Comments

Jonathan Cameron June 26, 2019, 6:34 p.m. UTC | #1
On Tue, 25 Jun 2019 16:13:25 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> Some devices like the ADIS16460 IMU require a stall period between
> transfers, i.e. between when the CS is de-asserted and re-asserted. The
> default value of 10us is not enough. This change makes the delay
> configurable for when the next CS change goes active.
> 
> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>

General principle seems fine to me, though naming may need some work.

cs_low_time or something more specific than stall perhaps?

+CC Mark.

> ---
>  drivers/spi/spi.c       | 3 ++-
>  include/linux/spi/spi.h | 3 +++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 5e75944ad5d1..739de0118ee1 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1163,7 +1163,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
>  				keep_cs = true;
>  			} else {
>  				spi_set_cs(msg->spi, false);
> -				udelay(10);
> +				udelay(xfer->cs_change_stall_delay_us ?
> +				       xfer->cs_change_stall_delay_us : 10);
>  				spi_set_cs(msg->spi, true);
>  			}
>  		}
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 053abd22ad31..d23add3b4790 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -734,6 +734,8 @@ extern void spi_res_release(struct spi_controller *ctlr,
>   *      transfer. If 0 the default (from @spi_device) is used.
>   * @bits_per_word: select a bits_per_word other than the device default
>   *      for this transfer. If 0 the default (from @spi_device) is used.
> + * @cs_change_stall_delay_us: microseconds to delay between cs_change
> + * 	transfers.
>   * @cs_change: affects chipselect after this transfer completes
>   * @delay_usecs: microseconds to delay after this transfer before
>   *	(optionally) changing the chipselect status, then starting
> @@ -823,6 +825,7 @@ struct spi_transfer {
>  #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
>  	u8		bits_per_word;
>  	u8		word_delay_usecs;
> +	u8		cs_change_stall_delay_us;
>  	u16		delay_usecs;
>  	u32		speed_hz;
>  	u16		word_delay;
Alexandru Ardelean June 27, 2019, 1:29 p.m. UTC | #2
On Wed, 2019-06-26 at 19:34 +0100, Jonathan Cameron wrote:
> [External]
> 
> On Tue, 25 Jun 2019 16:13:25 +0300
> Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> 
> > Some devices like the ADIS16460 IMU require a stall period between
> > transfers, i.e. between when the CS is de-asserted and re-asserted. The
> > default value of 10us is not enough. This change makes the delay
> > configurable for when the next CS change goes active.
> > 
> > Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> 
> General principle seems fine to me, though naming may need some work.
> 
> cs_low_time or something more specific than stall perhaps?

I agree the naming could do some work.
It was one of the items [in this series] for which I was expecting a bit of a discussion.

Thanks
Alex

> 
> +CC Mark.
> 
> > ---
> >  drivers/spi/spi.c       | 3 ++-
> >  include/linux/spi/spi.h | 3 +++
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> > index 5e75944ad5d1..739de0118ee1 100644
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -1163,7 +1163,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
> >  				keep_cs = true;
> >  			} else {
> >  				spi_set_cs(msg->spi, false);
> > -				udelay(10);
> > +				udelay(xfer->cs_change_stall_delay_us ?
> > +				       xfer->cs_change_stall_delay_us : 10);
> >  				spi_set_cs(msg->spi, true);
> >  			}
> >  		}
> > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> > index 053abd22ad31..d23add3b4790 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -734,6 +734,8 @@ extern void spi_res_release(struct spi_controller *ctlr,
> >   *      transfer. If 0 the default (from @spi_device) is used.
> >   * @bits_per_word: select a bits_per_word other than the device default
> >   *      for this transfer. If 0 the default (from @spi_device) is used.
> > + * @cs_change_stall_delay_us: microseconds to delay between cs_change
> > + * 	transfers.
> >   * @cs_change: affects chipselect after this transfer completes
> >   * @delay_usecs: microseconds to delay after this transfer before
> >   *	(optionally) changing the chipselect status, then starting
> > @@ -823,6 +825,7 @@ struct spi_transfer {
> >  #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
> >  	u8		bits_per_word;
> >  	u8		word_delay_usecs;
> > +	u8		cs_change_stall_delay_us;
> >  	u16		delay_usecs;
> >  	u32		speed_hz;
> >  	u16		word_delay;
Mark Brown July 9, 2019, 2:12 p.m. UTC | #3
On Wed, Jun 26, 2019 at 07:34:38PM +0100, Jonathan Cameron wrote:
> On Tue, 25 Jun 2019 16:13:25 +0300
> Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> 
> > Some devices like the ADIS16460 IMU require a stall period between
> > transfers, i.e. between when the CS is de-asserted and re-asserted. The
> > default value of 10us is not enough. This change makes the delay
> > configurable for when the next CS change goes active.

This looks like cs_change_delay.

As documented in SubmittingPatches please send patches to the 
maintainers for the code you would like to change.  The normal kernel
workflow is that people apply patches from their inboxes, if they aren't
copied they are likely to not see the patch at all and it is much more
difficult to apply patches.
Alexandru Ardelean July 17, 2019, 11:37 a.m. UTC | #4
On Tue, 2019-07-09 at 15:12 +0100, Mark Brown wrote:
> On Wed, Jun 26, 2019 at 07:34:38PM +0100, Jonathan Cameron wrote:
> > On Tue, 25 Jun 2019 16:13:25 +0300
> > Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> > 
> > > Some devices like the ADIS16460 IMU require a stall period between
> > > transfers, i.e. between when the CS is de-asserted and re-asserted. The
> > > default value of 10us is not enough. This change makes the delay
> > > configurable for when the next CS change goes active.
> 
> This looks like cs_change_delay.
> 
> As documented in SubmittingPatches please send patches to the 
> maintainers for the code you would like to change.  The normal kernel
> workflow is that people apply patches from their inboxes, if they aren't
> copied they are likely to not see the patch at all and it is much more
> difficult to apply patches.

Ack.
[Sorry for the late reply; I'm balancing other stuff as well and terrible at it]

I'll probably update my practice to also include maintainers via --cc to `git send-email`.
Up until now, I would send emails to lists [as much as possible] and try to not include people directly.
My assumption was that the list is enough.

I'm still adjusting to how things get done in the various Linux kernel subsystems/subgroups.

Patch
diff mbox series

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 5e75944ad5d1..739de0118ee1 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1163,7 +1163,8 @@  static int spi_transfer_one_message(struct spi_controller *ctlr,
 				keep_cs = true;
 			} else {
 				spi_set_cs(msg->spi, false);
-				udelay(10);
+				udelay(xfer->cs_change_stall_delay_us ?
+				       xfer->cs_change_stall_delay_us : 10);
 				spi_set_cs(msg->spi, true);
 			}
 		}
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 053abd22ad31..d23add3b4790 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -734,6 +734,8 @@  extern void spi_res_release(struct spi_controller *ctlr,
  *      transfer. If 0 the default (from @spi_device) is used.
  * @bits_per_word: select a bits_per_word other than the device default
  *      for this transfer. If 0 the default (from @spi_device) is used.
+ * @cs_change_stall_delay_us: microseconds to delay between cs_change
+ * 	transfers.
  * @cs_change: affects chipselect after this transfer completes
  * @delay_usecs: microseconds to delay after this transfer before
  *	(optionally) changing the chipselect status, then starting
@@ -823,6 +825,7 @@  struct spi_transfer {
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
 	u8		bits_per_word;
 	u8		word_delay_usecs;
+	u8		cs_change_stall_delay_us;
 	u16		delay_usecs;
 	u32		speed_hz;
 	u16		word_delay;