[1/4,V3] spi: Add optional stall delay between cs_change transfers
diff mbox series

Message ID 20190722124747.4792-2-alexandru.ardelean@analog.com
State Superseded
Headers show
Series
  • iio: imu: Add support for the ADIS16460 IMU
Related show

Commit Message

Alexandru Ardelean July 22, 2019, 12:47 p.m. UTC
Some devices like the ADIS16460 IMU require a longer 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, allowing the default
to remain 10us is case it is unspecified.

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 | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

Comments

Mark Brown July 22, 2019, 4:32 p.m. UTC | #1
On Mon, Jul 22, 2019 at 03:47:44PM +0300, Alexandru Ardelean wrote:
> Some devices like the ADIS16460 IMU require a longer 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, allowing the default
> to remain 10us is case it is unspecified.

For the third time:

| This looks like cs_change_delay.

>  #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
>  	u8		bits_per_word;
>  	u8		word_delay_usecs;
> +	u8		cs_change_delay;
>  	u16		delay_usecs;
>  	u32		speed_hz;
>  	u16		word_delay;

This patch doesn't apply and even if it did it won't compile because you
are trying to add a field with the same name as an existing one.
Alexandru Ardelean July 22, 2019, 7:27 p.m. UTC | #2
On Mon, Jul 22, 2019 at 8:42 PM Mark Brown <broonie@kernel.org> wrote:
>
> On Mon, Jul 22, 2019 at 03:47:44PM +0300, Alexandru Ardelean wrote:
> > Some devices like the ADIS16460 IMU require a longer 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, allowing the default
> > to remain 10us is case it is unspecified.
>
> For the third time:
>
> | This looks like cs_change_delay.
>
> >  #define      SPI_NBITS_QUAD          0x04 /* 4bits transfer */
> >       u8              bits_per_word;
> >       u8              word_delay_usecs;
> > +     u8              cs_change_delay;
> >       u16             delay_usecs;
> >       u32             speed_hz;
> >       u16             word_delay;
>
> This patch doesn't apply and even if it did it won't compile because you
> are trying to add a field with the same name as an existing one.

oooohhhhhhhh
now i see;

well, my fault here;
i was basing my patchset on top of branch iio/togreg from Jonathan's
tree for the IMU:
https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/log/?h=togreg
[ typically that's the base branch for new IIO drivers ]

that one is a bit behind, and does not contain the cs_change_delay
stuff you mentioned;
also, i will admit that sometimes, some review comments are not
completely obvious to me;
i should have checked the SPI tree before opening my mouth, but this
will [hopefully] serve me as a learning experience when sending
multi-subsystem patches
when sending to a single subsystem, it's clear; when sending to 2, i
get a bit lost

i do feel a bit bad for the noise i caused, but it's not the worst
thing i did today

anyway: disregard this, and i will sync with Jonathan about how to
proceed with this patch just for IIO;

thanks for your time and sorry for the noise
Alex

Patch
diff mbox series

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 5e75944ad5d1..fe7fa7fb25c5 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_delay ?
+				       xfer->cs_change_delay : 10);
 				spi_set_cs(msg->spi, true);
 			}
 		}
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 053abd22ad31..6de287f8e465 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -734,6 +734,7 @@  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_delay: 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 +824,7 @@  struct spi_transfer {
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
 	u8		bits_per_word;
 	u8		word_delay_usecs;
+	u8		cs_change_delay;
 	u16		delay_usecs;
 	u32		speed_hz;
 	u16		word_delay;