linux-kernel - Re: [PATCH 2/2] drivers: phy: qcom: ipq806x-usb: conver latch function to pool macro

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Date:   Sun, 23 Jan 2022 15:46:25 +0100
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drivers: phy: qcom: ipq806x-usb: conver latch
 function to pool macro

On Sun, Jan 23, 2022 at 05:22:18PM +0530, Vinod Koul wrote:
> On 17-01-22, 01:26, Ansuel Smith wrote:
> > Convert latch function to readl pool macro to tidy things up.
> > 
> > Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> > ---
> >  drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c | 17 +++++------------
> >  1 file changed, 5 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c b/drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c
> > index 6788e0e8272a..ab2d1431546d 100644
> > --- a/drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c
> > +++ b/drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c
> > @@ -112,6 +112,9 @@
> >  #define SS_CR_READ_REG				BIT(0)
> >  #define SS_CR_WRITE_REG				BIT(0)
> >  
> > +#define LATCH_SLEEP				40
> > +#define LATCH_TIMEOUT				100
> > +
> >  struct usb_phy {
> >  	void __iomem		*base;
> >  	struct device		*dev;
> > @@ -156,19 +159,9 @@ static inline void usb_phy_write_readback(struct usb_phy *phy_dwc3,
> >  
> >  static int wait_for_latch(void __iomem *addr)
> >  {
> > -	u32 retry = 10;
> > -
> > -	while (true) {
> > -		if (!readl(addr))
> > -			break;
> 
> we break if read returns non zero value...
> 
> Do you know what is the value expected?
>

If I understand the logic here, we write a value and we wait for it to
get applied. To confirm that we execute a writel and then we readl the
same address until it does return a value. That is the way used to
understand that the write process has finished and that the value has
been applied/we can write again.

> > -
> > -		if (--retry == 0)
> > -			return -ETIMEDOUT;
> > -
> > -		usleep_range(10, 20);
> > -	}
> > +	u32 val;
> 
> Okay this contains garbage..

I think I didn't understand, val value will get replaced by readl in
the pool_timeout function.

> >  
> > -	return 0;
> > +	return readl_poll_timeout(addr, val, !val, LATCH_SLEEP, LATCH_TIMEOUT);
> 
> and we are waiting for it read a garbage value!
> 

Again could be very confused and wrong but the pool_timeout macro does
the exact same thing of the wait_for_latch function with th only
difference of handling the sleep differently. We put in val the return
of readl and the break condition as !val. Or I didn't understand the
concern about garbage value.

> 
> -- 
> ~Vinod

-- 
	Ansuel