[PATCH] w1: w1-gpio: Loosen timings to improve cold boot reliability

[Chris Morgan]

On Mon, Nov 22, 2021 at 11:16:22AM +0000, Eugen.Hristev at microchip.com wrote:
> On 11/8/21 5:07 PM, Chris Morgan wrote:
> > From: Chris Morgan <macromorgan at hotmail.com>
> > 
> > On my NTC CHIP whenever I do a cold boot any attached DIPs cannot be
> > found. Rebooting on the other hand appears to fix the issue. I found
> > that if I modified the timing slightly (but still within spec) the
> > w1 identification on cold boot became far more reliable.
> > 
> > Signed-off-by: Chris Morgan <macromorgan at hotmail.com>
> > ---
> >   drivers/w1/w1-gpio.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/w1/w1-gpio.c b/drivers/w1/w1-gpio.c
> > index 9346f810ce..5565de2a92 100644
> > --- a/drivers/w1/w1-gpio.c
> > +++ b/drivers/w1/w1-gpio.c
> > @@ -22,8 +22,8 @@
> >   #define W1_TIMING_E    9
> >   #define W1_TIMING_F    55
> >   #define W1_TIMING_G    0
> > -#define W1_TIMING_H    480
> > -#define W1_TIMING_I    70
> > +#define W1_TIMING_H    600
> > +#define W1_TIMING_I    100
> >   #define W1_TIMING_J    410
> > 
> >   struct w1_gpio_pdata {
> > --
> > 2.30.2
> > 
> 
> 
> Hi Chris,
> 
> I tested your patch on my board sama5d2_xplained, and it works.
> Thus, you can add my
> Tested-by: Eugen Hristev <eugen.hristev at microchip.com>
> 
> However, I disagree with the changes you did in timings. What I found 
> was that timing 'H' could go up to 640 , but timing 'I' to a maximum of 
> 75 or so. [1]
> 
> I am thinking maybe you could also check your udelays with a scope on 
> the 1wire line ? Because your problem might be in fact in some other 
> part , like udelays not properly aligned/synchronized/accurate at cold 
> boot time, depending on the source of clock you are using.

I lack a scope, but will extensively test 640 and 75 as the new timings.
Would that be acceptable?

Thank you.

> 
> Eugen
> 
> 
> [1] 
> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.maximintegrated.com%2Fcontent%2Fdam%2Ffiles%2Fdesign%2Ftools%2Ftech-docs%2F126%2FAN126-timing-calculation.zip&data=04%7C01%7C%7C6787b70951c4494fd76808d9ada98a17%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637731765952771191%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=V81HrXrKI8d45WTrvWrc6ydJy2rdCX5%2FL8eYjvxcwCs%3D&reserved=0