[PATCH 0/2] Use master-abort for slave probes

[PATCH 0/2] Use master-abort for slave probes

[Russell King - ARM Linux admin]

Hi,

This series allows us to use the "master abort" feature when probing
slaves rather than resetting the controller, which allows more
graceful recovery to bus free state after sending the address byte.

The i2c-pxa controller expects to send data after the address byte
rather than a stop.  Rather than resetting the bus (and thus forcing
a bus-free state by releasing the SCL line) which may leave the bus
in an indeterminant state, use the master-abort command instead.

This patch series applies on top of the previous posted cleanup patches,
although it may also apply to -rc.

 drivers/i2c/busses/i2c-pxa.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

-- 
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[PATCH 1/2] i2c: pxa: clear all master action bits in i2c_pxa_stop_message()

[Russell King]

If we timeout during a message transfer, the control register may
contain bits that cause an action to be set. Read-modify-writing the
register leaving these bits set may trigger the hardware to attempt
one of these actions unintentionally.

Always clear these bits when cleaning up after a message or after
a timeout.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/i2c/busses/i2c-pxa.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-pxa.c b/drivers/i2c/busses/i2c-pxa.c
index db739cce93ac..a72d07bdb793 100644
--- a/drivers/i2c/busses/i2c-pxa.c
+++ b/drivers/i2c/busses/i2c-pxa.c
@@ -795,11 +795,9 @@ static inline void i2c_pxa_stop_message(struct pxa_i2c *i2c)
 {
 	u32 icr;
 
-	/*
-	 * Clear the STOP and ACK flags
-	 */
+	/* Clear the START, STOP, ACK, TB and MA flags */
 	icr = readl(_ICR(i2c));
-	icr &= ~(ICR_STOP | ICR_ACKNAK);
+	icr &= ~(ICR_START | ICR_STOP | ICR_ACKNAK | ICR_TB | ICR_MA);
 	writel(icr, _ICR(i2c));
 }
 
-- 
2.20.1

Re: [PATCH 1/2] i2c: pxa: clear all master action bits in i2c_pxa_stop_message()

[Wolfram Sang]

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On Wed, May 06, 2020 at 10:36:38AM +0100, Russell King wrote:
> If we timeout during a message transfer, the control register may
> contain bits that cause an action to be set. Read-modify-writing the
> register leaving these bits set may trigger the hardware to attempt
> one of these actions unintentionally.
> 
> Always clear these bits when cleaning up after a message or after
> a timeout.
> 
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Applied to for-next, thanks! I was considering for-current, though, but
there have been no real bug reports, so for-next it is.


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[PATCH 2/2] i2c: pxa: use master-abort for device probes

[Russell King]

Use master-abort to send the stop condition after an address cycle
rather than resetting the controller.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/i2c/busses/i2c-pxa.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-pxa.c b/drivers/i2c/busses/i2c-pxa.c
index a72d07bdb793..0e194d6cd1b5 100644
--- a/drivers/i2c/busses/i2c-pxa.c
+++ b/drivers/i2c/busses/i2c-pxa.c
@@ -940,14 +940,8 @@ static void i2c_pxa_irq_txempty(struct pxa_i2c *i2c, u32 isr)
 		icr &= ~ICR_ALDIE;
 		icr |= ICR_START | ICR_TB;
 	} else {
-		if (i2c->msg->len == 0) {
-			/*
-			 * Device probes have a message length of zero
-			 * and need the bus to be reset before it can
-			 * be used again.
-			 */
-			i2c_pxa_reset(i2c);
-		}
+		if (i2c->msg->len == 0)
+			icr |= ICR_MA;
 		i2c_pxa_master_complete(i2c, 0);
 	}
 
-- 
2.20.1

Re: [PATCH 2/2] i2c: pxa: use master-abort for device probes

[Wolfram Sang]

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On Wed, May 06, 2020 at 10:36:43AM +0100, Russell King wrote:
> Use master-abort to send the stop condition after an address cycle
> rather than resetting the controller.
> 
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Applied to for-next, thanks!


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