Re: Re: [PATCH v2 2/2] bus: sunxi-rsb: Support atomic transfers

Jernej Škrabec
2022-11-07T18:11:26Z

Dne ponedeljek, 07. november 2022 ob 12:30:29 CET je Andre Przywara
napisal(a):
> On Sun, 6 Nov 2022 23:22:00 -0600
> Samuel Holland <samuel@sholland.org> wrote:
>
> Hi,
>
> > When communicating with a PMIC during system poweroff (pm_power_off()),
> > IRQs are disabled and we are in a RCU read-side critical section, so we
> > cannot use wait_for_completion_io_timeout(). Instead, poll the status
> > register for transfer completion.
> >
> > Fixes: d787dcdb9c8f ("bus: sunxi-rsb: Add driver for Allwinner Reduced
> > Serial Bus") Signed-off-by: Samuel Holland <samuel@sholland.org>
> > ---
> >
> > Changes in v2:
> > - Add Fixes tag to patch 2
> > - Only check for specific status bits when polling
> >
> > drivers/bus/sunxi-rsb.c | 27 ++++++++++++++++++++-------
> > 1 file changed, 20 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
> > index 17343cd75338..012e82f9b7b0 100644
> > --- a/drivers/bus/sunxi-rsb.c
> > +++ b/drivers/bus/sunxi-rsb.c
> > @@ -267,6 +267,9 @@ EXPORT_SYMBOL_GPL(sunxi_rsb_driver_register);
> >
> > /* common code that starts a transfer */
> > static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
> > {
> >
> > + u32 int_mask, status;
> > + bool timeout;
> > +
> >
> > if (readl(rsb->regs + RSB_CTRL) & RSB_CTRL_START_TRANS) {
> >
> > dev_dbg(rsb->dev, "RSB transfer still in progress\n");
> > return -EBUSY;
> >
> > @@ -274,13 +277,23 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb
> > *rsb)
> >
> > reinit_completion(&rsb->complete);
> >
> > - writel(RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR |
RSB_INTS_TRANS_OVER,
> > + int_mask = RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR |
RSB_INTS_TRANS_OVER;
> > + writel(int_mask,
> >
> > rsb->regs + RSB_INTE);
> >
> > writel(RSB_CTRL_START_TRANS | RSB_CTRL_GLOBAL_INT_ENB,
> >
> > rsb->regs + RSB_CTRL);
> >
> > - if (!wait_for_completion_io_timeout(&rsb->complete,
> > -
msecs_to_jiffies(100))) {
> > + if (irqs_disabled()) {
> > + timeout = readl_poll_timeout_atomic(rsb->regs +
RSB_INTS,
> > + status,
(status & int_mask),
> > + 10,
100000);
>
> So if I understand correctly, this mimics the operation of
> sunxi_rsb_irq(), just replacing rsb->status with status.
> But wouldn't that also mean that we need to clear the interrupt bits in
> INTS, since we are about to handle them below?

Yes, I pointed out that in review of v1.

Best regards,
Jernej

>
> It probably doesn't matter in practise, since we call this during power
> down only, but looks like more robust to do, from a driver's perspective.
>
> Cheers,
> Andre
>
> > + } else {
> > + timeout = !wait_for_completion_io_timeout(&rsb-
>complete,
> > +
msecs_to_jiffies(100));
> > + status = rsb->status;
> > + }
> > +
> > + if (timeout) {
> >
> > dev_dbg(rsb->dev, "RSB timeout\n");
> >
> > /* abort the transfer */
> >
> > @@ -292,18 +305,18 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb
> > *rsb)
> >
> > return -ETIMEDOUT;
> >
> > }
> >
> > - if (rsb->status & RSB_INTS_LOAD_BSY) {
> > + if (status & RSB_INTS_LOAD_BSY) {
> >
> > dev_dbg(rsb->dev, "RSB busy\n");
> > return -EBUSY;
> >
> > }
> >
> > - if (rsb->status & RSB_INTS_TRANS_ERR) {
> > - if (rsb->status & RSB_INTS_TRANS_ERR_ACK) {
> > + if (status & RSB_INTS_TRANS_ERR) {
> > + if (status & RSB_INTS_TRANS_ERR_ACK) {
> >
> > dev_dbg(rsb->dev, "RSB slave nack\n");
> > return -EINVAL;
> >
> > }
> >
> > - if (rsb->status & RSB_INTS_TRANS_ERR_DATA) {
> > + if (status & RSB_INTS_TRANS_ERR_DATA) {
> >
> > dev_dbg(rsb->dev, "RSB transfer data
error\n");
> > return -EIO;
> >
> > }