[PATCH v3 REBASED] spi: Add capability to perform some transfer with chipselect off

[PATCH v3 REBASED] spi: Add capability to perform some transfer with chipselect off

[Christophe Leroy]

Some components require a few clock cycles with chipselect off before
or/and after the data transfer done with CS on.

Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
should have one cycle before CS goes low, and two cycles after
CS goes high".

The cycles "before" are implicitely provided by all previous activity
on the SPI bus. But the cycles "after" must be provided in order to
terminate the SPI transfer.

In order to use that kind of component, add a cs_off flag to
spi_transfer struct. When this flag is set, the transfer is performed
with chipselect off. This allows consummer to add a dummy transfer
at the end of the transfer list which is performed with chipselect
OFF, providing the required additional clock cycles.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
Rebased on today's linus' master

 drivers/spi/spi.c       | 12 +++++++++---
 include/linux/spi/spi.h |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 83da8862b8f2..cc5cb948978e 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1435,7 +1435,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 	struct spi_statistics __percpu *statm = ctlr->pcpu_statistics;
 	struct spi_statistics __percpu *stats = msg->spi->pcpu_statistics;
 
-	spi_set_cs(msg->spi, true, false);
+	xfer = list_first_entry(&msg->transfers, struct spi_transfer, transfer_list);
+	spi_set_cs(msg->spi, !xfer->cs_off, false);
 
 	SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
 	SPI_STATISTICS_INCREMENT_FIELD(stats, messages);
@@ -1503,10 +1504,15 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 					 &msg->transfers)) {
 				keep_cs = true;
 			} else {
-				spi_set_cs(msg->spi, false, false);
+				if (!xfer->cs_off)
+					spi_set_cs(msg->spi, false, false);
 				_spi_transfer_cs_change_delay(msg, xfer);
-				spi_set_cs(msg->spi, true, false);
+				if (!list_next_entry(xfer, transfer_list)->cs_off)
+					spi_set_cs(msg->spi, true, false);
 			}
+		} else if (!list_is_last(&xfer->transfer_list, &msg->transfers) &&
+			   xfer->cs_off != list_next_entry(xfer, transfer_list)->cs_off) {
+			spi_set_cs(msg->spi, xfer->cs_off, false);
 		}
 
 		msg->actual_length += xfer->len;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index e6c73d5ff1a8..6e6c62c59957 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -847,6 +847,7 @@ struct spi_res {
  *      for this transfer. If 0 the default (from @spi_device) is used.
  * @dummy_data: indicates transfer is dummy bytes transfer.
  * @cs_change: affects chipselect after this transfer completes
+ * @cs_off: performs the transfer with chipselect off.
  * @cs_change_delay: delay between cs deassert and assert when
  *      @cs_change is set and @spi_transfer is not the last in @spi_message
  * @delay: delay to be introduced after this transfer before
@@ -959,6 +960,7 @@ struct spi_transfer {
 	unsigned	cs_change:1;
 	unsigned	tx_nbits:3;
 	unsigned	rx_nbits:3;
+	unsigned	cs_off:1;
 #define	SPI_NBITS_SINGLE	0x01 /* 1bit transfer */
 #define	SPI_NBITS_DUAL		0x02 /* 2bits transfer */
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
-- 
2.37.1

[PATCH v3 REBASED] spi: Add capability to perform some transfer with chipselect off

[Christophe Leroy]

Some components require a few clock cycles with chipselect off before
or/and after the data transfer done with CS on.

Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
should have one cycle before CS goes low, and two cycles after
CS goes high".

The cycles "before" are implicitely provided by all previous activity
on the SPI bus. But the cycles "after" must be provided in order to
terminate the SPI transfer.

In order to use that kind of component, add a cs_off flag to
spi_transfer struct. When this flag is set, the transfer is performed
with chipselect off. This allows consummer to add a dummy transfer
at the end of the transfer list which is performed with chipselect
OFF, providing the required additional clock cycles.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
Rebased on today's linus' master

 drivers/spi/spi.c       | 12 +++++++++---
 include/linux/spi/spi.h |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 83da8862b8f2..cc5cb948978e 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1435,7 +1435,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 	struct spi_statistics __percpu *statm = ctlr->pcpu_statistics;
 	struct spi_statistics __percpu *stats = msg->spi->pcpu_statistics;
 
-	spi_set_cs(msg->spi, true, false);
+	xfer = list_first_entry(&msg->transfers, struct spi_transfer, transfer_list);
+	spi_set_cs(msg->spi, !xfer->cs_off, false);
 
 	SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
 	SPI_STATISTICS_INCREMENT_FIELD(stats, messages);
@@ -1503,10 +1504,15 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 					 &msg->transfers)) {
 				keep_cs = true;
 			} else {
-				spi_set_cs(msg->spi, false, false);
+				if (!xfer->cs_off)
+					spi_set_cs(msg->spi, false, false);
 				_spi_transfer_cs_change_delay(msg, xfer);
-				spi_set_cs(msg->spi, true, false);
+				if (!list_next_entry(xfer, transfer_list)->cs_off)
+					spi_set_cs(msg->spi, true, false);
 			}
+		} else if (!list_is_last(&xfer->transfer_list, &msg->transfers) &&
+			   xfer->cs_off != list_next_entry(xfer, transfer_list)->cs_off) {
+			spi_set_cs(msg->spi, xfer->cs_off, false);
 		}
 
 		msg->actual_length += xfer->len;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index e6c73d5ff1a8..6e6c62c59957 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -847,6 +847,7 @@ struct spi_res {
  *      for this transfer. If 0 the default (from @spi_device) is used.
  * @dummy_data: indicates transfer is dummy bytes transfer.
  * @cs_change: affects chipselect after this transfer completes
+ * @cs_off: performs the transfer with chipselect off.
  * @cs_change_delay: delay between cs deassert and assert when
  *      @cs_change is set and @spi_transfer is not the last in @spi_message
  * @delay: delay to be introduced after this transfer before
@@ -959,6 +960,7 @@ struct spi_transfer {
 	unsigned	cs_change:1;
 	unsigned	tx_nbits:3;
 	unsigned	rx_nbits:3;
+	unsigned	cs_off:1;
 #define	SPI_NBITS_SINGLE	0x01 /* 1bit transfer */
 #define	SPI_NBITS_DUAL		0x02 /* 2bits transfer */
 #define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
-- 
2.37.1

Re: [PATCH v3 REBASED] spi: Add capability to perform some transfer with chipselect off

[Mark Brown]

On Wed, 7 Sep 2022 16:11:25 +0200, Christophe Leroy wrote:
> Some components require a few clock cycles with chipselect off before
> or/and after the data transfer done with CS on.
> 
> Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
> should have one cycle before CS goes low, and two cycles after
> CS goes high".
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: Add capability to perform some transfer with chipselect off
      commit: 5e0531f6b90ac096fedaf5bd0eae0bb4e5a39da5

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

Re: [PATCH v3 REBASED] spi: Add capability to perform some transfer with chipselect off

[Andy Shevchenko]

On Wed, Sep 07, 2022 at 04:13:44PM +0200, Christophe Leroy wrote:
> Some components require a few clock cycles with chipselect off before
> or/and after the data transfer done with CS on.
> 
> Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
> should have one cycle before CS goes low, and two cycles after
> CS goes high".
> 
> The cycles "before" are implicitely provided by all previous activity
> on the SPI bus. But the cycles "after" must be provided in order to
> terminate the SPI transfer.
> 
> In order to use that kind of component, add a cs_off flag to
> spi_transfer struct. When this flag is set, the transfer is performed
> with chipselect off. This allows consummer to add a dummy transfer
> at the end of the transfer list which is performed with chipselect
> OFF, providing the required additional clock cycles.

Interesting. Wondering if this helps to improve mmc-spi.c case, which
abuses SPI protocol on the initialisation phase.

P.S> just noticed this change in the Git history of spi.c changes :-)

-- 
With Best Regards,
Andy Shevchenko