spi: spi-fsl-dspi: Add GPIO chip select support

Commit Message

Maksim Kiselev Dec. 3, 2020, 5:12 p.m. UTC

From: Maxim Kiselev <[e-mail]>
Date: Thu, 3 Dec 2020 18:56:12 +0300
Subject: [PATCH] spi: spi-fsl-dspi: Add GPIO chip select support

This patch allows use of GPIO for the chip select.
Because dSPI controller can't send transactions without hardware chip
selects, so first unused native CS will be set in SPI_PUSHR_CMD_PCS

Signed-off-by: Maxim Kiselev <[e-mail]>
---
 drivers/spi/spi-fsl-dspi.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

             /* Leave PCS activated after last transfer when
@@ -1240,6 +1245,7 @@ static int dspi_probe(struct platform_device *pdev)
     dspi->pdev = pdev;
     dspi->ctlr = ctlr;

+    ctlr->use_gpio_descriptors = true;
     ctlr->setup = dspi_setup;
     ctlr->transfer_one_message = dspi_transfer_one_message;
     ctlr->dev.of_node = pdev->dev.of_node;

Comments

Vladimir Oltean Dec. 3, 2020, 5:50 p.m. UTC | #1

Hi Maxim,

On Thu, Dec 03, 2020 at 08:12:19PM +0300, Максим Киселёв wrote:
> From: Maxim Kiselev <[e-mail]>
> Date: Thu, 3 Dec 2020 18:56:12 +0300
> Subject: [PATCH] spi: spi-fsl-dspi: Add GPIO chip select support
> 
> This patch allows use of GPIO for the chip select.
> Because dSPI controller can't send transactions without hardware chip
> selects, so first unused native CS will be set in SPI_PUSHR_CMD_PCS

Are you sure?

From the reference manual:

SPIx_PUSHR bits 10–15 PCS:
Select which PCS signals are to be asserted for the transfer. Refer to
the chip-specific SPI information for the number of PCS signals used in
this chip.
0 Negate the PCS[x] signal.
1 Assert the PCS[x] signal.

And the definition is:

#define SPI_PUSHR_CMD_PCS(x)		(BIT(x) & GENMASK(5, 0))

Notice the BIT(x).

I expect that you can set the PCS to 0 and no hard chip select will
assert.

Maksim Kiselev Dec. 3, 2020, 6:50 p.m. UTC | #2

Hi Vladimir, thanks for the answer!

I must have missed these. In any case, I would like to add
functionality for using GPIO as CS. Because I have a board which
actually uses this. I'II check your solution and modify my patch.

чт, 3 дек. 2020 г. в 20:50, Vladimir Oltean <[e-mail]>:
>
> Hi Maxim,
>
> On Thu, Dec 03, 2020 at 08:12:19PM +0300, Максим Киселёв wrote:
> > From: Maxim Kiselev <[e-mail]>
> > Date: Thu, 3 Dec 2020 18:56:12 +0300
> > Subject: [PATCH] spi: spi-fsl-dspi: Add GPIO chip select support
> >
> > This patch allows use of GPIO for the chip select.
> > Because dSPI controller can't send transactions without hardware chip
> > selects, so first unused native CS will be set in SPI_PUSHR_CMD_PCS
>
> Are you sure?
>
> From the reference manual:
>
> SPIx_PUSHR bits 10–15 PCS:
> Select which PCS signals are to be asserted for the transfer. Refer to
> the chip-specific SPI information for the number of PCS signals used in
> this chip.
> 0 Negate the PCS[x] signal.
> 1 Assert the PCS[x] signal.
>
> And the definition is:
>
> #define SPI_PUSHR_CMD_PCS(x)            (BIT(x) & GENMASK(5, 0))
>
> Notice the BIT(x).
>
> I expect that you can set the PCS to 0 and no hard chip select will
> assert.

Vladimir Oltean Dec. 4, 2020, 1:05 a.m. UTC | #3

On Thu, Dec 03, 2020 at 09:50:04PM +0300, Maksim Kiselev wrote:
> In any case, I would like to add functionality for using GPIO as CS.
> Because I have a board which actually uses this.

I have absolutely nothing to object to that.
But the patches should still be as clean as possible, though.

Patch

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 028736687488..d5fba34de740 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -913,9 +913,14 @@  static int dspi_transfer_one_message(struct
spi_controller *ctlr,
         dspi->cur_transfer = transfer;
         dspi->cur_msg = message;
         dspi->cur_chip = spi_get_ctldata(spi);
+
+        if (spi->cs_gpiod)
+            gpiod_set_value(spi->cs_gpiod, 1);
+
         /* Prepare command word for CMD FIFO */
         dspi->tx_cmd = SPI_PUSHR_CMD_CTAS(0) |
-                   SPI_PUSHR_CMD_PCS(spi->chip_select);
+                   SPI_PUSHR_CMD_PCS(spi->cs_gpiod ?
+                         ctlr->unused_native_cs : spi->chip_select);
         if (list_is_last(&dspi->cur_transfer->transfer_list,
                  &dspi->cur_msg->transfers)) {