diff mbox

SPI: BCM2835: enable support of 3-wire mode

Message ID 1426755714-28130-4-git-send-email-kernel@martin.sperl.org (mailing list archive)
State Accepted
Commit 6935224da2482a261c786501fbccb1dc4a675225
Headers show

Commit Message

Martin Sperl March 19, 2015, 9:01 a.m. UTC 
From: Martin Sperl <kernel@martin.sperl.org>

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
---
 drivers/spi/spi-bcm2835.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

Stephen Warren March 20, 2015, 5:12 a.m. UTC | #1 
On 03/19/2015 03:01 AM, kernel@martin.sperl.org wrote:

> diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c

> @@ -201,6 +202,9 @@ static int bcm2835_spi_start_transfer(
>  		cdiv = 0; /* 0 is the slowest we can go */
>  	}
>  
> +	if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf))
> +		cs |= BCM2835_SPI_CS_REN;
> +

I can see how that tells the HW which direction to transfer data in
3WIRE mode, but how does the HW know whether it's in 3WIRE mode or has
separate RX/TX lines?
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Martin Sperl March 20, 2015, 6:17 a.m. UTC | #2 
> On 20.03.2015, at 06:12, Stephen Warren <swarren@wwwdotorg.org> wrote:
> I can see how that tells the HW which direction to transfer data in
> 3WIRE mode, but how does the HW know whether it's in 3WIRE mode or has
> separate RX/TX lines?

The HW assumes with this flag that MISO (=RX) sits on the same physical
line as MOSI (=TX). This flag essentially just changes directions of
the TX GPIO pin from out to in and samples the level on the TX pin.

Without this patch what you would need to do to make such a device
work is connecting RX with TX and that with the MIMO pin of the final
device (maybe add a pullup). This flag is essentially just a shortcut.

Note that the SPI-framework does the testing so that either RX or TX
can be set in SPI-3WIRE mode (not both).

Ciao,
	Martin



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Mark Brown March 23, 2015, 6:57 p.m. UTC | #3 
On Thu, Mar 19, 2015 at 09:01:53AM +0000, kernel@martin.sperl.org wrote:
> From: Martin Sperl <kernel@martin.sperl.org>
> 
> Signed-off-by: Martin Sperl <kernel@martin.sperl.org>

Applied, thanks.
diff mbox

Patch

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index e1dea40..51883f8 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -67,7 +67,8 @@ 
 #define BCM2835_SPI_CS_CS_01		0x00000001
 
 #define BCM2835_SPI_TIMEOUT_MS	30000
-#define BCM2835_SPI_MODE_BITS	(SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_NO_CS)
+#define BCM2835_SPI_MODE_BITS	(SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \
+				| SPI_NO_CS | SPI_3WIRE)
 
 #define DRV_NAME	"spi-bcm2835"
 
@@ -201,6 +202,9 @@  static int bcm2835_spi_start_transfer(
 		cdiv = 0; /* 0 is the slowest we can go */
 	}
 
+	if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf))
+		cs |= BCM2835_SPI_CS_REN;
+
 	if (spi->mode & SPI_CPOL)
 		cs |= BCM2835_SPI_CS_CPOL;
 	if (spi->mode & SPI_CPHA)