Ensure Low period of SCL is correct

[PATCH 0/3] Ensure Low period of SCL is correct

Posted by Lucas Tanure 4 years, 2 months ago

The default duty cycle of 33% is less than the required
by the I2C specs for the LOW period of the SCL clock.

So, for 100Khz or less, use 50%H/50%L duty cycle, and
for the clock above 100Khz, use 40%H/60%L duty cycle.
That ensures the low period of SCL is always more than
the minimum required by the specs at any given frequency.

Lucas Tanure (3):
  i2c: meson: Use _SHIFT and _MASK for register definitions
  i2c: meson: Use 50% duty cycle for I2C clock
  i2c: meson: Remove meson_i2c_data

 drivers/i2c/busses/i2c-meson.c | 104 ++++++++++++++++++---------------
 1 file changed, 56 insertions(+), 48 deletions(-)

-- 
2.35.1

Re: [PATCH 0/3] Ensure Low period of SCL is correct

Posted by Kevin Hilman 4 years, 2 months ago

Hi Lucas,

Lucas Tanure <tanure@linux.com> writes:

> The default duty cycle of 33% is less than the required
> by the I2C specs for the LOW period of the SCL clock.
>
> So, for 100Khz or less, use 50%H/50%L duty cycle, and
> for the clock above 100Khz, use 40%H/60%L duty cycle.
> That ensures the low period of SCL is always more than
> the minimum required by the specs at any given frequency.

Thanks for the fixes!

This is going to affect all SoCs, so ould you please summarize how your
changes were tested, and on which SoCs & boards?

Thanks,

Kevin

Re: [PATCH 0/3] Ensure Low period of SCL is correct

Posted by Lucas Tanure 4 years, 2 months ago

On Mon, 28 Mar 2022, 21:37 Kevin Hilman, <khilman@baylibre.com> wrote:
>
> Hi Lucas,
>
> Lucas Tanure <tanure@linux.com> writes:
>
> > The default duty cycle of 33% is less than the required
> > by the I2C specs for the LOW period of the SCL clock.
> >
> > So, for 100Khz or less, use 50%H/50%L duty cycle, and
> > for the clock above 100Khz, use 40%H/60%L duty cycle.
> > That ensures the low period of SCL is always more than
> > the minimum required by the specs at any given frequency.
>
> Thanks for the fixes!
>
> This is going to affect all SoCs, so ould you please summarize how your
> changes were tested, and on which SoCs & boards?
>
> Thanks,
>
> Kevin

Hi,

I only tested against the vim3 board, measured the bus with a Saleae
logic pro 16.
The measurements were with 100k, 400k, and a few in-between frequencies.

Is that enough?

Thanks
Lucas

Re: [PATCH 0/3] Ensure Low period of SCL is correct

Posted by Neil Armstrong 4 years, 2 months ago

Hi,

On 29/03/2022 00:31, Lucas Tanure wrote:
> On Mon, 28 Mar 2022, 21:37 Kevin Hilman, <khilman@baylibre.com> wrote:
>>
>> Hi Lucas,
>>
>> Lucas Tanure <tanure@linux.com> writes:
>>
>>> The default duty cycle of 33% is less than the required
>>> by the I2C specs for the LOW period of the SCL clock.
>>>
>>> So, for 100Khz or less, use 50%H/50%L duty cycle, and
>>> for the clock above 100Khz, use 40%H/60%L duty cycle.
>>> That ensures the low period of SCL is always more than
>>> the minimum required by the specs at any given frequency.
>>
>> Thanks for the fixes!
>>
>> This is going to affect all SoCs, so ould you please summarize how your
>> changes were tested, and on which SoCs & boards?
>>
>> Thanks,
>>
>> Kevin
> 
> Hi,
> 
> I only tested against the vim3 board, measured the bus with a Saleae
> logic pro 16.
> The measurements were with 100k, 400k, and a few in-between frequencies.

Thanks, it's a great addition to have !

> 
> Is that enough?

A test on GXL/GXM (VIM1 or VIM2) & GXBB (Odroid-C2) devices is lacking before we
can merge this.

If I find some time, I'll have a try, but everyone is welcome testing this serie
and report if it still works fine for them.

Vyacheslav, do you think you can test on your JetHub devices ? it would validate GXL & AXG.

Neil

> 
> Thanks
> Lucas

Re: [PATCH 0/3] Ensure Low period of SCL is correct

Posted by Vyacheslav 4 years, 2 months ago


04.04.2022 11:01, Neil Armstrong wrote:
> Hi,
> 
> On 29/03/2022 00:31, Lucas Tanure wrote:
>> On Mon, 28 Mar 2022, 21:37 Kevin Hilman, <khilman@baylibre.com> wrote:
>>>
>>> Hi Lucas,
>>>
>>> Lucas Tanure <tanure@linux.com> writes:
>>>
>>>> The default duty cycle of 33% is less than the required
>>>> by the I2C specs for the LOW period of the SCL clock.
>>>>
>>>> So, for 100Khz or less, use 50%H/50%L duty cycle, and
>>>> for the clock above 100Khz, use 40%H/60%L duty cycle.
>>>> That ensures the low period of SCL is always more than
>>>> the minimum required by the specs at any given frequency.
>>>
>>> Thanks for the fixes!
>>>
>>> This is going to affect all SoCs, so ould you please summarize how your
>>> changes were tested, and on which SoCs & boards?
>>>
>>> Thanks,
>>>
>>> Kevin
>>
>> Hi,
>>
>> I only tested against the vim3 board, measured the bus with a Saleae
>> logic pro 16.
>> The measurements were with 100k, 400k, and a few in-between frequencies.
> 
> Thanks, it's a great addition to have !
> 
>>
>> Is that enough?
> 
> A test on GXL/GXM (VIM1 or VIM2) & GXBB (Odroid-C2) devices is lacking 
> before we
> can merge this.
> 
> If I find some time, I'll have a try, but everyone is welcome testing 
> this serie
> and report if it still works fine for them.
> 
> Vyacheslav, do you think you can test on your JetHub devices ? it would 
> validate GXL & AXG.

It builds ok on 5.17. JetHub H1/D1 has only rtc clock (pcf8563) and 
1-wire controller (ds2482) on i2c bus. I did't see any difference with 
or without patches. all works at first look.

Vyacheslav