[PATCH v2 0/1] i2c: omap: correct usage of the interrupt enable register

[PATCH v2 0/1] i2c: omap: correct usage of the interrupt enable register

[Oleksandr Dmytryshyn]

I've just added a detailed description of the problem that is being solved
to the cover letter and commit message in the patch.

If the i2c controller during suspend will generate an interrupt, it
can lead to unpredictable behaviour in the kernel.

Based on the logic of the kernel code interrupts from i2c should be
prohibited during suspend. Kernel writes 0 to the I2C_IE register in
the omap_i2c_runtime_suspend() function. In the other side kernel
writes saved interrupt flags to the I2C_IE register in
omap_i2c_runtime_resume() function. I.e. interrupts should be disabled
during suspend.

This works for chips with version1 registers scheme. Interrupts are
disabled during suspend. For chips with version2 scheme registers
writting 0 to the I2C_IE register does nothing (because now the
I2C_IRQENABLE_SET register is located at this address). This register
is used to enable interrupts. For disabling interrupts
I2C_IRQENABLE_CLR register should be used.

Because the registers I2C_IRQENABLE_SET and I2C_IE have the same
addresses, the interrupt enabling procedure is unchanged.

I've checked that interrupts in the i2c controller are still enabled
after writting 0 to the I2C_IE register. But with my patch interrupts
are disabled in the omap_i2c_runtime_suspend() function. 

Next patch fixes it.

Patch is based on:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tag: v3.10-rc2

Verified on OMAP4430.

Oleksandr Dmytryshyn (1):
  i2c: omap: correct usage of the interrupt enable register

 drivers/i2c/busses/i2c-omap.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

-- 
1.8.2.rc2

[PATCH v2 1/1] i2c: omap: correct usage of the interrupt enable register

[Oleksandr Dmytryshyn]

If the i2c controller during suspend will generate an interrupt, it
can lead to unpredictable behaviour in the kernel.

Based on the logic of the kernel code interrupts from i2c should be
prohibited during suspend. Kernel writes 0 to the I2C_IE register in
the omap_i2c_runtime_suspend() function. In the other side kernel
writes saved interrupt flags to the I2C_IE register in
omap_i2c_runtime_resume() function. I.e. interrupts should be disabled
during suspend.

This works for chips with version1 registers scheme. Interrupts are
disabled during suspend. For chips with version2 scheme registers
writting 0 to the I2C_IE register does nothing (because now the
I2C_IRQENABLE_SET register is located at this address). This register
is used to enable interrupts. For disabling interrupts
I2C_IRQENABLE_CLR register should be used.

Because the registers I2C_IRQENABLE_SET and I2C_IE have the same
addresses, the interrupt enabling procedure is unchanged.

Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org>
---
 drivers/i2c/busses/i2c-omap.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index e02f9e3..2419899 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -180,6 +180,8 @@ enum {
 #define I2C_OMAP_ERRATA_I207		(1 << 0)
 #define I2C_OMAP_ERRATA_I462		(1 << 1)
 
+#define OMAP_I2C_INTERRUPTS_MASK	0x6FFF
+
 struct omap_i2c_dev {
 	spinlock_t		lock;		/* IRQ synchronization */
 	struct device		*dev;
@@ -193,6 +195,7 @@ struct omap_i2c_dev {
 						    long latency);
 	u32			speed;		/* Speed of bus in kHz */
 	u32			flags;
+	u16			scheme;
 	u16			cmd_err;
 	u8			*buf;
 	u8			*regs;
@@ -1082,7 +1085,7 @@ omap_i2c_probe(struct platform_device *pdev)
 	int irq;
 	int r;
 	u32 rev;
-	u16 minor, major, scheme;
+	u16 minor, major;
 
 	/* NOTE: driver uses the static register mapping */
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -1159,8 +1162,8 @@ omap_i2c_probe(struct platform_device *pdev)
 	 */
 	rev = __raw_readw(dev->base + 0x04);
 
-	scheme = OMAP_I2C_SCHEME(rev);
-	switch (scheme) {
+	dev->scheme = OMAP_I2C_SCHEME(rev);
+	switch (dev->scheme) {
 	case OMAP_I2C_SCHEME_0:
 		dev->regs = (u8 *)reg_map_ip_v1;
 		dev->rev = omap_i2c_read_reg(dev, OMAP_I2C_REV_REG);
@@ -1289,7 +1292,11 @@ static int omap_i2c_runtime_suspend(struct device *dev)
 
 	_dev->iestate = omap_i2c_read_reg(_dev, OMAP_I2C_IE_REG);
 
-	omap_i2c_write_reg(_dev, OMAP_I2C_IE_REG, 0);
+	if (_dev->scheme == OMAP_I2C_SCHEME_0)
+		omap_i2c_write_reg(_dev, OMAP_I2C_IE_REG, 0);
+	else
+		omap_i2c_write_reg(_dev, OMAP_I2C_IP_V2_IRQENABLE_CLR,
+				   OMAP_I2C_INTERRUPTS_MASK);
 
 	if (_dev->rev < OMAP_I2C_OMAP1_REV_2) {
 		omap_i2c_read_reg(_dev, OMAP_I2C_IV_REG); /* Read clears */
-- 
1.8.2.rc2

Re: [PATCH v2 1/1] i2c: omap: correct usage of the interrupt enable register

[Kevin Hilman]

Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org> writes:

> If the i2c controller during suspend will generate an interrupt, it
> can lead to unpredictable behaviour in the kernel.
>
> Based on the logic of the kernel code interrupts from i2c should be
> prohibited during suspend. Kernel writes 0 to the I2C_IE register in
> the omap_i2c_runtime_suspend() function. In the other side kernel
> writes saved interrupt flags to the I2C_IE register in
> omap_i2c_runtime_resume() function. I.e. interrupts should be disabled
> during suspend.
>
> This works for chips with version1 registers scheme. Interrupts are
> disabled during suspend. For chips with version2 scheme registers
> writting 0 to the I2C_IE register does nothing (because now the
> I2C_IRQENABLE_SET register is located at this address). This register
> is used to enable interrupts. For disabling interrupts
> I2C_IRQENABLE_CLR register should be used.
>
> Because the registers I2C_IRQENABLE_SET and I2C_IE have the same
> addresses, the interrupt enabling procedure is unchanged.
>
> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org>

Much better, but still doesn't explain how/why this has been working up
until now.  Have we just been lucky?

> ---
>  drivers/i2c/busses/i2c-omap.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index e02f9e3..2419899 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -180,6 +180,8 @@ enum {
>  #define I2C_OMAP_ERRATA_I207		(1 << 0)
>  #define I2C_OMAP_ERRATA_I462		(1 << 1)
>  
> +#define OMAP_I2C_INTERRUPTS_MASK	0x6FFF

To be more clear, this should probably have v2 in the name.

Kevin

Re: [PATCH v2 1/1] i2c: omap: correct usage of the interrupt enable register

[Oleksandr Dmytryshyn]

On 05/30/2013 07:46 PM, Kevin Hilman wrote:
> Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org> writes:
>
>> If the i2c controller during suspend will generate an interrupt, it
>> can lead to unpredictable behaviour in the kernel.
>>
>> Based on the logic of the kernel code interrupts from i2c should be
>> prohibited during suspend. Kernel writes 0 to the I2C_IE register in
>> the omap_i2c_runtime_suspend() function. In the other side kernel
>> writes saved interrupt flags to the I2C_IE register in
>> omap_i2c_runtime_resume() function. I.e. interrupts should be disabled
>> during suspend.
>>
>> This works for chips with version1 registers scheme. Interrupts are
>> disabled during suspend. For chips with version2 scheme registers
>> writting 0 to the I2C_IE register does nothing (because now the
>> I2C_IRQENABLE_SET register is located at this address). This register
>> is used to enable interrupts. For disabling interrupts
>> I2C_IRQENABLE_CLR register should be used.
>>
>> Because the registers I2C_IRQENABLE_SET and I2C_IE have the same
>> addresses, the interrupt enabling procedure is unchanged.
>>
>> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org>
> Much better, but still doesn't explain how/why this has been working up
> until now.  Have we just been lucky?
Yes, this has been working up until now because we've just been lucky.
>
>> ---
>>   drivers/i2c/busses/i2c-omap.c | 15 +++++++++++----
>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
>> index e02f9e3..2419899 100644
>> --- a/drivers/i2c/busses/i2c-omap.c
>> +++ b/drivers/i2c/busses/i2c-omap.c
>> @@ -180,6 +180,8 @@ enum {
>>   #define I2C_OMAP_ERRATA_I207		(1 << 0)
>>   #define I2C_OMAP_ERRATA_I462		(1 << 1)
>>   
>> +#define OMAP_I2C_INTERRUPTS_MASK	0x6FFF
> To be more clear, this should probably have v2 in the name.
I'll rename this mask in the patch-set v3
>
> Kevin
>


-- 

Best regards,
Oleksandr Dmytryshyn | OMAP4 Platform
GlobalLogic Inc. | Innovation by Design

Re: [PATCH v2 1/1] i2c: omap: correct usage of the interrupt enable register

[Kevin Hilman]

Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org> writes:

> On 05/30/2013 07:46 PM, Kevin Hilman wrote:
>> Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org> writes:
>>
>>> If the i2c controller during suspend will generate an interrupt, it
>>> can lead to unpredictable behaviour in the kernel.
>>>
>>> Based on the logic of the kernel code interrupts from i2c should be
>>> prohibited during suspend. Kernel writes 0 to the I2C_IE register in
>>> the omap_i2c_runtime_suspend() function. In the other side kernel
>>> writes saved interrupt flags to the I2C_IE register in
>>> omap_i2c_runtime_resume() function. I.e. interrupts should be disabled
>>> during suspend.
>>>
>>> This works for chips with version1 registers scheme. Interrupts are
>>> disabled during suspend. For chips with version2 scheme registers
>>> writting 0 to the I2C_IE register does nothing (because now the
>>> I2C_IRQENABLE_SET register is located at this address). This register
>>> is used to enable interrupts. For disabling interrupts
>>> I2C_IRQENABLE_CLR register should be used.
>>>
>>> Because the registers I2C_IRQENABLE_SET and I2C_IE have the same
>>> addresses, the interrupt enabling procedure is unchanged.
>>>
>>> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn-l0cyMroinI0@public.gmane.org>
>> Much better, but still doesn't explain how/why this has been working up
>> until now.  Have we just been lucky?
> Yes, this has been working up until now because we've just been lucky.

What I'm trying to say is you need to describe that in the changelog,
with more details.  e.g. we've been lucky not to have any interrupts
fire during the suspend path, otherwise we would have....

Kevin


>>
>>> ---
>>>   drivers/i2c/busses/i2c-omap.c | 15 +++++++++++----
>>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
>>> index e02f9e3..2419899 100644
>>> --- a/drivers/i2c/busses/i2c-omap.c
>>> +++ b/drivers/i2c/busses/i2c-omap.c
>>> @@ -180,6 +180,8 @@ enum {
>>>   #define I2C_OMAP_ERRATA_I207		(1 << 0)
>>>   #define I2C_OMAP_ERRATA_I462		(1 << 1)
>>>   +#define OMAP_I2C_INTERRUPTS_MASK	0x6FFF
>> To be more clear, this should probably have v2 in the name.
> I'll rename this mask in the patch-set v3
>>
>> Kevin
>>