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

From: "Jernej Škrabec" <jernej.skrabec@gmail.com>
To: Chen-Yu Tsai <wens@csie.org>, Samuel Holland <samuel@sholland.org>
Cc: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, Samuel Holland <samuel@sholland.org>
Subject: Re: [PATCH 2/2] bus: sunxi-rsb: Support atomic transfers
Date: Sat, 05 Nov 2022 20:48:35 +0100	[thread overview]
Message-ID: <4752203.GXAFRqVoOG@jernej-laptop> (raw)
In-Reply-To: <4779430.31r3eYUQgx@jernej-laptop>

Dne sobota, 05. november 2022 ob 20:46:47 CET je Jernej Škrabec napisal(a):
> Dne sobota, 05. november 2022 ob 20:19:53 CET je Samuel Holland napisal(a):
> > 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.
> > 
> > Signed-off-by: Samuel Holland <samuel@sholland.org>

Also a fixes tag would be in order here.

Best regards,
Jernej

> > ---
> > 
> >  drivers/bus/sunxi-rsb.c | 23 +++++++++++++++++------
> >  1 file changed, 17 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
> > index 17343cd75338..0f0e498d4379 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)
> >  {
> > 
> > +	bool timeout;
> > +	u32 status;
> > +
> > 
> >  	if (readl(rsb->regs + RSB_CTRL) & RSB_CTRL_START_TRANS) {
> >  	
> >  		dev_dbg(rsb->dev, "RSB transfer still in progress\n");
> >  		return -EBUSY;
> > 
> > @@ -279,8 +282,16 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
> > 
> >  	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, 10, 100000);
> 
> It would be good to check only for RSB_INTS_LOAD_BSY, RSB_INTS_TRANS_ERR and
> RSB_INTS_TRANS_OVER flags and clear them afterwards. That way we avoid
> problems if this path is used outside power off case.
> 
> Best regards,
> Jernej
> 
> > +	} 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 +303,18 @@ 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;
> >  		
> >  		}

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