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

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Message-ID: <20170206143555.jo7y57y7gjw3ialm@rfolt0960.corp.atmel.com>
Date:   Mon, 6 Feb 2017 15:35:55 +0100
From:   Ludovic Desroches <ludovic.desroches@...rochip.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:     Wolfram Sang <wsa@...-dreams.de>,
        Ludovic Desroches <ludovic.desroches@...el.com>,
        <linux-i2c@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Cyrille Pitchen <cyrille.pitchen@...rochip.com>
Subject: Re: [PATCH] i2c: at91: ensure state is restored after suspending

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@...e-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
>