linux-kernel - Re: [PATCH v3 3/3] bus: sunxi-rsb: Clear interrupt status before each transfer

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Message-ID: <1910101.PYKUYFuaPT@jernej-laptop>
Date:   Tue, 15 Nov 2022 22:38:29 +0100
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>, Samuel Holland <samuel@...lland.org>
Cc:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...ts.linux.dev,
        Andre Przywara <andre.przywara@....com>
Subject: Re: [PATCH v3 3/3] bus: sunxi-rsb: Clear interrupt status before each transfer

Dne torek, 15. november 2022 ob 07:08:12 CET je Samuel Holland napisal(a):
> On 11/14/22 15:00, Jernej Škrabec wrote:
> > Hi Samuel,
> > 
> > Dne ponedeljek, 14. november 2022 ob 02:57:49 CET je Samuel Holland
> > 
> > napisal(a):
> >> Currently, the driver clears the interrupt status bits after anything
> >> could have set them. However, this requires duplicating the same logic
> >> in several places.
> >> 
> >> Instead of clearing the status flags in the interrupt handler, disable
> >> all further interrupts by clearing the RSB_CTRL_GLOBAL_INT_ENB bit.
> > 
> > where is this bit cleared?
> 
> It is cleared by any write to RSB_CTRL that does not include it. I noted
> it below with the "disable interrupts" comments.

Right.

> 
> >> Then we can delay the status register write until the start of the next
> >> transfer, so it only has to be done in one place.
> >> 
> >> Signed-off-by: Samuel Holland <samuel@...lland.org>
> >> ---
> >> 
> >> Changes in v3:
> >>  - Add a patch refactoring how the status bits are cleared
> >>  
> >>  drivers/bus/sunxi-rsb.c | 20 +++++---------------
> >>  1 file changed, 5 insertions(+), 15 deletions(-)
> >> 
> >> diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
> >> index 3aa91aed3bf7..cb622e60897b 100644
> >> --- a/drivers/bus/sunxi-rsb.c
> >> +++ b/drivers/bus/sunxi-rsb.c
> >> @@ -279,6 +279,7 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
> >> 
> >>  	int_mask = RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR |
> >>  	RSB_INTS_TRANS_OVER;
> >>  	writel(int_mask, rsb->regs + RSB_INTE);
> >> 
> >> +	writel(int_mask, rsb->regs + RSB_INTS);
> > 
> > Wouldn't be better to clear status before enabling interrupts? Unless
> > global interrupt flag is cleared beforehand, but I don't see that
> > anywhere.
> Indeed the intention was that the global interrupt flag is cleared
> beforehand, and only enabled on the next line below. However, I realize
> I missed disabling it for the new atomic case.
> 
> I'm not so sure anymore that this patch is an improvement. What do you
> think? I can send a v4 with a fix, or I am fine with skipping this
> patch. I would at least like the other two to be merged for -fixes.

Sure, first two patches will go in regardless. I'm not convinced of value of 
this patch either. I guess we can skip it.

Best regards,
Jernej

> 
> Regards,
> Samuel
> 
> >>  	writel(RSB_CTRL_START_TRANS | RSB_CTRL_GLOBAL_INT_ENB,
> >>  	
> >>  	       rsb->regs + RSB_CTRL);
> >> 
> >> @@ -286,7 +287,6 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
> >> 
> >>  		timeout = readl_poll_timeout_atomic(rsb->regs + 
RSB_INTS,
> >>  		
> >>  						    
status, (status & int_mask),
> >>  						    10, 
100000);
> >> 
> >> -		writel(status, rsb->regs + RSB_INTS);
> >> 
> >>  	} else {
> >>  	
> >>  		timeout = !wait_for_completion_io_timeout(&rsb-
> >> 
> >> complete,
> >> 
> >>  							
  msecs_to_jiffies(100));
> >> 
> >> @@ -296,12 +296,9 @@ static int _sunxi_rsb_run_xfer(struct sunxi_rsb
> >> *rsb)
> >> 
> >>  	if (timeout) {
> >>  	
> >>  		dev_dbg(rsb->dev, "RSB timeout\n");
> >> 
> >> -		/* abort the transfer */
> >> +		/* abort the transfer and disable interrupts */
> >> 
> >>  		writel(RSB_CTRL_ABORT_TRANS, rsb->regs + RSB_CTRL);
> >> 
> >> -		/* clear any interrupt flags */
> >> -		writel(readl(rsb->regs + RSB_INTS), rsb->regs + 
RSB_INTS);
> >> -
> >> 
> >>  		return -ETIMEDOUT;
> >>  	
> >>  	}
> >> 
> >> @@ -503,15 +500,11 @@ EXPORT_SYMBOL_GPL(__devm_regmap_init_sunxi_rsb);
> >> 
> >>  static irqreturn_t sunxi_rsb_irq(int irq, void *dev_id)
> >>  {
> >>  
> >>  	struct sunxi_rsb *rsb = dev_id;
> >> 
> >> -	u32 status;
> >> 
> >> -	status = readl(rsb->regs + RSB_INTS);
> >> -	rsb->status = status;
> >> +	/* disable interrupts */
> >> +	writel(0, rsb->regs + RSB_CTRL);
> >> 
> >> -	/* Clear interrupts */
> >> -	status &= (RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR |
> >> -		   RSB_INTS_TRANS_OVER);
> >> -	writel(status, rsb->regs + RSB_INTS);
> >> +	rsb->status = readl(rsb->regs + RSB_INTS);
> >> 
> >>  	complete(&rsb->complete);
> >> 
> >> @@ -532,9 +525,6 @@ static int sunxi_rsb_init_device_mode(struct
> >> sunxi_rsb
> >> *rsb) if (reg & RSB_DMCR_DEVICE_START)
> >> 
> >>  		ret = -ETIMEDOUT;
> >> 
> >> -	/* clear interrupt status bits */
> >> -	writel(readl(rsb->regs + RSB_INTS), rsb->regs + RSB_INTS);
> >> -
> >> 
> >>  	return ret;
> >>  
> >>  }