[PATCH] i2c: at91: ensure state is restored after suspending

[PATCH] i2c: at91: ensure state is restored after suspending

[Alexandre Belloni]

When going to suspend, the I2C registers may be lost because the power to
VDDcore is cut. Save them and restore them when resuming.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 drivers/i2c/busses/i2c-at91.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index 0b86c6173e07..633bdd899952 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -140,6 +140,12 @@ struct at91_twi_dev {
 	unsigned transfer_status;
 	struct i2c_adapter adapter;
 	unsigned twi_cwgr_reg;
+	struct {
+		u32 mmr;
+		u32 imr;
+		u32 fmr;
+		u32 fimr;
+	} cache;
 	struct at91_twi_pdata *pdata;
 	bool use_dma;
 	bool use_alt_cmd;
@@ -1172,6 +1178,15 @@ static int at91_twi_runtime_resume(struct device *dev)
 
 static int at91_twi_suspend_noirq(struct device *dev)
 {
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
+
+	twi_dev->cache.mmr = at91_twi_read(twi_dev, AT91_TWI_MMR);
+	twi_dev->cache.imr = at91_twi_read(twi_dev, AT91_TWI_IMR);
+	if (twi_dev->fifo_size) {
+		twi_dev->cache.fmr = at91_twi_read(twi_dev, AT91_TWI_FMR);
+		twi_dev->cache.fimr = at91_twi_read(twi_dev, AT91_TWI_FIMR);
+	}
+
 	if (!pm_runtime_status_suspended(dev))
 		at91_twi_runtime_suspend(dev);
 
@@ -1180,6 +1195,7 @@ static int at91_twi_suspend_noirq(struct device *dev)
 
 static int at91_twi_resume_noirq(struct device *dev)
 {
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
 	int ret;
 
 	if (!pm_runtime_status_suspended(dev)) {
@@ -1191,6 +1207,14 @@ static int at91_twi_resume_noirq(struct device *dev)
 	pm_runtime_mark_last_busy(dev);
 	pm_request_autosuspend(dev);
 
+	at91_init_twi_bus(twi_dev);
+	at91_twi_write(twi_dev, AT91_TWI_MMR, twi_dev->cache.mmr);
+	at91_twi_write(twi_dev, AT91_TWI_IER, twi_dev->cache.imr);
+	if (twi_dev->fifo_size) {
+		at91_twi_write(twi_dev, AT91_TWI_FMR, twi_dev->cache.fmr);
+		at91_twi_write(twi_dev, AT91_TWI_FIER, twi_dev->cache.fimr);
+	}
+
 	return 0;
 }
 
-- 
2.11.0

Re: [PATCH] i2c: at91: ensure state is restored after suspending

[Wolfram Sang]

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> +	at91_init_twi_bus(twi_dev);

Can't this function reinit the registers to the needed values? I am not
convinced that a cache will always reflect the proper state after
resume.


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Re: [PATCH] i2c: at91: ensure state is restored after suspending

[Ludovic Desroches]

Hi,

I add Cyrille for FIFO part.

On Mon, Jan 30, 2017 at 06:25:33PM +0100, Alexandre Belloni wrote:
> When going to suspend, the I2C registers may be lost because the power to
> VDDcore is cut. Save them and restore them when resuming.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> ---
>  drivers/i2c/busses/i2c-at91.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index 0b86c6173e07..633bdd899952 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -140,6 +140,12 @@ struct at91_twi_dev {
>  	unsigned transfer_status;
>  	struct i2c_adapter adapter;
>  	unsigned twi_cwgr_reg;
> +	struct {
> +		u32 mmr;
> +		u32 imr;
> +		u32 fmr;
> +		u32 fimr;
> +	} cache;

Do we really need it?

For instance MMR is only written in at91_twi_xfer(). I am not sure we can
continue the transfer when resuming. I assume we will need to perform a new
transfer from a proper state.

Moreover at91_init_twi_bus() is called on resume, it will perform a reset and
it seems it can lead to strange behaviors:
"Note that issuing a software while transmitting might leave a slave in
an unknown state holding the TWD line. In such case, a Bus Clear Command
will allow to make the slave release the TWD line (the first frame
sent afterwards might not be received properly by the slave)."

I think fimr is useless, AT91_TWI_FIER and AT91_TWI_FIDR are not used in
the current code.

Regards

Ludovic

>  	struct at91_twi_pdata *pdata;
>  	bool use_dma;
>  	bool use_alt_cmd;
> @@ -1172,6 +1178,15 @@ static int at91_twi_runtime_resume(struct device *dev)
>  
>  static int at91_twi_suspend_noirq(struct device *dev)
>  {
> +	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
> +
> +	twi_dev->cache.mmr = at91_twi_read(twi_dev, AT91_TWI_MMR);
> +	twi_dev->cache.imr = at91_twi_read(twi_dev, AT91_TWI_IMR);
> +	if (twi_dev->fifo_size) {
> +		twi_dev->cache.fmr = at91_twi_read(twi_dev, AT91_TWI_FMR);
> +		twi_dev->cache.fimr = at91_twi_read(twi_dev, AT91_TWI_FIMR);
> +	}
> +
>  	if (!pm_runtime_status_suspended(dev))
>  		at91_twi_runtime_suspend(dev);
>  
> @@ -1180,6 +1195,7 @@ static int at91_twi_suspend_noirq(struct device *dev)
>  
>  static int at91_twi_resume_noirq(struct device *dev)
>  {
> +	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
>  	int ret;
>  
>  	if (!pm_runtime_status_suspended(dev)) {
> @@ -1191,6 +1207,14 @@ static int at91_twi_resume_noirq(struct device *dev)
>  	pm_runtime_mark_last_busy(dev);
>  	pm_request_autosuspend(dev);
>  
> +	at91_init_twi_bus(twi_dev);
> +	at91_twi_write(twi_dev, AT91_TWI_MMR, twi_dev->cache.mmr);
> +	at91_twi_write(twi_dev, AT91_TWI_IER, twi_dev->cache.imr);
> +	if (twi_dev->fifo_size) {
> +		at91_twi_write(twi_dev, AT91_TWI_FMR, twi_dev->cache.fmr);
> +		at91_twi_write(twi_dev, AT91_TWI_FIER, twi_dev->cache.fimr);
> +	}
> +
>  	return 0;
>  }
>  
> -- 
> 2.11.0
> 

Re: [PATCH] i2c: at91: ensure state is restored after suspending

[Alexandre Belloni]

On 06/02/2017 at 15:35:55 +0100, Ludovic Desroches wrote:
> On Mon, Jan 30, 2017 at 06:25:33PM +0100, Alexandre Belloni wrote:
> > When going to suspend, the I2C registers may be lost because the power to
> > VDDcore is cut. Save them and restore them when resuming.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> > ---
> >  drivers/i2c/busses/i2c-at91.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> > index 0b86c6173e07..633bdd899952 100644
> > --- a/drivers/i2c/busses/i2c-at91.c
> > +++ b/drivers/i2c/busses/i2c-at91.c
> > @@ -140,6 +140,12 @@ struct at91_twi_dev {
> >  	unsigned transfer_status;
> >  	struct i2c_adapter adapter;
> >  	unsigned twi_cwgr_reg;
> > +	struct {
> > +		u32 mmr;
> > +		u32 imr;
> > +		u32 fmr;
> > +		u32 fimr;
> > +	} cache;
> 
> Do we really need it?
> 
> For instance MMR is only written in at91_twi_xfer(). I am not sure we can
> continue the transfer when resuming. I assume we will need to perform a new
> transfer from a proper state.
> 
> Moreover at91_init_twi_bus() is called on resume, it will perform a reset and
> it seems it can lead to strange behaviors:
> "Note that issuing a software while transmitting might leave a slave in
> an unknown state holding the TWD line. In such case, a Bus Clear Command
> will allow to make the slave release the TWD line (the first frame
> sent afterwards might not be received properly by the slave)."
> 

Yeah, so basically because VDDcore is cut, we are not in a position
where continuing the transfer is possible.

I would simply call at91_init_twi_bus() in resume_noirq. I think it is
the proper thing to do.

> I think fimr is useless, AT91_TWI_FIER and AT91_TWI_FIDR are not used in
> the current code.
> 

You are right.

> Regards
> 
> Ludovic
> 
> >  	struct at91_twi_pdata *pdata;
> >  	bool use_dma;
> >  	bool use_alt_cmd;
> > @@ -1172,6 +1178,15 @@ static int at91_twi_runtime_resume(struct device *dev)
> >  
> >  static int at91_twi_suspend_noirq(struct device *dev)
> >  {
> > +	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
> > +
> > +	twi_dev->cache.mmr = at91_twi_read(twi_dev, AT91_TWI_MMR);
> > +	twi_dev->cache.imr = at91_twi_read(twi_dev, AT91_TWI_IMR);
> > +	if (twi_dev->fifo_size) {
> > +		twi_dev->cache.fmr = at91_twi_read(twi_dev, AT91_TWI_FMR);
> > +		twi_dev->cache.fimr = at91_twi_read(twi_dev, AT91_TWI_FIMR);
> > +	}
> > +
> >  	if (!pm_runtime_status_suspended(dev))
> >  		at91_twi_runtime_suspend(dev);
> >  
> > @@ -1180,6 +1195,7 @@ static int at91_twi_suspend_noirq(struct device *dev)
> >  
> >  static int at91_twi_resume_noirq(struct device *dev)
> >  {
> > +	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
> >  	int ret;
> >  
> >  	if (!pm_runtime_status_suspended(dev)) {
> > @@ -1191,6 +1207,14 @@ static int at91_twi_resume_noirq(struct device *dev)
> >  	pm_runtime_mark_last_busy(dev);
> >  	pm_request_autosuspend(dev);
> >  
> > +	at91_init_twi_bus(twi_dev);
> > +	at91_twi_write(twi_dev, AT91_TWI_MMR, twi_dev->cache.mmr);
> > +	at91_twi_write(twi_dev, AT91_TWI_IER, twi_dev->cache.imr);
> > +	if (twi_dev->fifo_size) {
> > +		at91_twi_write(twi_dev, AT91_TWI_FMR, twi_dev->cache.fmr);
> > +		at91_twi_write(twi_dev, AT91_TWI_FIER, twi_dev->cache.fimr);
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > -- 
> > 2.11.0
> > 

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com