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

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