[PATCHv2 1/2] Documentation: dt: spi: Add GPIO Slave Select Parameter

[PATCHv2 1/2] Documentation: dt: spi: Add GPIO Slave Select Parameter

[tthayer]

From: Thor Thayer <tthayer@opensource.altera.com>

Some SPI masters require the slave to be selected before a
transaction can occur - even in the case of GPIO chip select.

This patch adds a GPIO slave select parameter to indicate
the slave needs to be selected in the GPIO CS case.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
---
v2  Add to SPI framework - add bindings.
---
 Documentation/devicetree/bindings/spi/spi-bus.txt |    1 +
 1 file changed, 1 insertion(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 4b1d6e7..3a006bc 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -24,6 +24,7 @@ support describing the chip select layout.
 Optional properties:
 - cs-gpios	  - gpios chip select.
 - num-cs	  - total number of chipselects.
+- gpio-ss	  - use internal slave select with gpio chip select.
 
 If cs-gpios is used the number of chip selects will be increased automatically
 with max(cs-gpios > hw cs).
-- 
1.7.9.5

[PATCHv2 2/2] spi: Add Flag to Enable Slave Select with GPIO Chip Select.

[tthayer-yzvPICuk2ABMcg4IHK0kFoH6Mc4MB0Vx]

From: Thor Thayer <tthayer-yzvPICuk2ABMcg4IHK0kFoH6Mc4MB0Vx@public.gmane.org>

Some SPI masters require slave selection before the transfer
can begin [1]. The SPI framework currently selects the chip using
either 1) the internal CS mechanism or 2) the GPIO CS, but not both.

This patch adds a boolean variable to indicate both the GPIO CS and
the internal chip select should be used.

Tested On:
    Altera CycloneV development kit
    Compile tested for build errors on x86_64 (allyesconfigs)

[1] DesignWare dw_apb_ssi Databook, Version 3.20a (page 39)

Signed-off-by: Thor Thayer <tthayer-yzvPICuk2ABMcg4IHK0kFoH6Mc4MB0Vx@public.gmane.org>
---
v2  Move changes to SPI framework based on maintainer comments
    Add a new SPI master boolean variable.
---
 drivers/spi/spi.c       |   10 ++++++++--
 include/linux/spi/spi.h |    1 +
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 5787b72..c042a8c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -697,10 +697,14 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
 	if (spi->mode & SPI_CS_HIGH)
 		enable = !enable;
 
-	if (gpio_is_valid(spi->cs_gpio))
+	if (gpio_is_valid(spi->cs_gpio)) {
 		gpio_set_value(spi->cs_gpio, !enable);
-	else if (spi->master->set_cs)
+		/* Some SPI masters need both GPIO CS & slave_select */
+		if (spi->master->set_cs && spi->master->gpio_ss)
+			spi->master->set_cs(spi, !enable);
+	} else if (spi->master->set_cs) {
 		spi->master->set_cs(spi, !enable);
+	}
 }
 
 #ifdef CONFIG_HAS_DMA
@@ -1845,6 +1849,8 @@ static int of_spi_register_master(struct spi_master *master)
 	for (i = 0; i < nb; i++)
 		cs[i] = of_get_named_gpio(np, "cs-gpios", i);
 
+	master->gpio_ss = of_property_read_bool(np, "gpio-ss");
+
 	return 0;
 }
 #else
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 4b743ac..0437995 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -551,6 +551,7 @@ struct spi_master {
 
 	/* gpio chip select */
 	int			*cs_gpios;
+	bool			gpio_ss;
 
 	/* statistics */
 	struct spi_statistics	statistics;
-- 
1.7.9.5

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Re: [PATCHv2 1/2] Documentation: dt: spi: Add GPIO Slave Select Parameter

[Geert Uytterhoeven]

On Fri, Oct 7, 2016 at 4:56 PM,  <tthayer@opensource.altera.com> wrote:
> From: Thor Thayer <tthayer@opensource.altera.com>
>
> Some SPI masters require the slave to be selected before a
> transaction can occur - even in the case of GPIO chip select.
>
> This patch adds a GPIO slave select parameter to indicate
> the slave needs to be selected in the GPIO CS case.
>
> Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
> ---
> v2  Add to SPI framework - add bindings.
> ---
>  Documentation/devicetree/bindings/spi/spi-bus.txt |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
> index 4b1d6e7..3a006bc 100644
> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
> @@ -24,6 +24,7 @@ support describing the chip select layout.
>  Optional properties:
>  - cs-gpios       - gpios chip select.
>  - num-cs         - total number of chipselects.
> +- gpio-ss        - use internal slave select with gpio chip select.
>
>  If cs-gpios is used the number of chip selects will be increased automatically
>  with max(cs-gpios > hw cs).

To me, this looks more like a new flag the SPI controller driver should
set in spi_master.flags, instead of a DT property.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCHv2 1/2] Documentation: dt: spi: Add GPIO Slave Select Parameter

[Thor Thayer]

On 10/07/2016 02:33 PM, Geert Uytterhoeven wrote:
> On Fri, Oct 7, 2016 at 4:56 PM,  <tthayer@opensource.altera.com> wrote:
>> From: Thor Thayer <tthayer@opensource.altera.com>
>>
>> Some SPI masters require the slave to be selected before a
>> transaction can occur - even in the case of GPIO chip select.
>>
>> This patch adds a GPIO slave select parameter to indicate
>> the slave needs to be selected in the GPIO CS case.
>>
>> Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
>> ---
>> v2  Add to SPI framework - add bindings.
>> ---
>>  Documentation/devicetree/bindings/spi/spi-bus.txt |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> index 4b1d6e7..3a006bc 100644
>> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
>> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> @@ -24,6 +24,7 @@ support describing the chip select layout.
>>  Optional properties:
>>  - cs-gpios       - gpios chip select.
>>  - num-cs         - total number of chipselects.
>> +- gpio-ss        - use internal slave select with gpio chip select.
>>
>>  If cs-gpios is used the number of chip selects will be increased automatically
>>  with max(cs-gpios > hw cs).
>
> To me, this looks more like a new flag the SPI controller driver should
> set in spi_master.flags, instead of a DT property.
>
Yes, I see your point since this is SPI master specific. I'll respin as 
you suggest.

Thanks for reviewing!

> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>