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

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Date:   Mon, 07 Nov 2022 19:05:33 +0100
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Samuel Holland <samuel@...lland.org>,
        Andre Przywara <andre.przywara@....com>
Cc:     Chen-Yu Tsai <wens@...e.org>, linux-arm-kernel@...ts.infradead.org,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: Re: [PATCH v2 2/2] bus: sunxi-rsb: Support atomic transfers

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@...lland.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@...lland.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;
> >  		
> >  		}