| Message ID | 1567418773-2427-3-git-send-email-eugen.hristev@microchip.com |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | i2c: add support for filters | expand |
| Context | Check | Description |
|---|---|---|
| robh/checkpatch | warning | "total: 0 errors, 1 warnings, 17 lines checked" |
On 2019-09-02 12:12, Eugen.Hristev@microchip.com wrote: > From: Eugen Hristev <eugen.hristev@microchip.com> > > Some i2c controllers have a built-in digital or analog filter. > This is specifically required depending on the hardware PCB/board. > Some controllers also allow specifying the maximum width of the > spikes that can be filtered. The width length can be specified in nanoseconds. > > Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com> > --- > Documentation/devicetree/bindings/i2c/i2c.txt | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt > index 44efafd..8dbff67 100644 > --- a/Documentation/devicetree/bindings/i2c/i2c.txt > +++ b/Documentation/devicetree/bindings/i2c/i2c.txt > @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below. > Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C > specification. > > +- i2c-analog-filter > + Enable analog filter for i2c lines. > + > +- i2c-digital-filter > + Enable digital filter for i2c lines. > + > +- i2c-filter-width-ns > + Width of spikes which can be filtered by either digital or analog > + filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified filtr -> filter (two instances) What if you want/need to have different bandwidth for the digital and analog filters? After all, this is a generic binding... Cheers, Peter > + in nanoseconds. > + > - interrupts > interrupts used by the device. > >
On 02.09.2019 13:49, Peter Rosin wrote: > On 2019-09-02 12:12, Eugen.Hristev@microchip.com wrote: >> From: Eugen Hristev <eugen.hristev@microchip.com> >> >> Some i2c controllers have a built-in digital or analog filter. >> This is specifically required depending on the hardware PCB/board. >> Some controllers also allow specifying the maximum width of the >> spikes that can be filtered. The width length can be specified in nanoseconds. >> >> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com> >> --- >> Documentation/devicetree/bindings/i2c/i2c.txt | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt >> index 44efafd..8dbff67 100644 >> --- a/Documentation/devicetree/bindings/i2c/i2c.txt >> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt >> @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below. >> Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C >> specification. >> >> +- i2c-analog-filter >> + Enable analog filter for i2c lines. >> + >> +- i2c-digital-filter >> + Enable digital filter for i2c lines. >> + >> +- i2c-filter-width-ns >> + Width of spikes which can be filtered by either digital or analog >> + filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified > > filtr -> filter (two instances) > > What if you want/need to have different bandwidth for the digital and analog > filters? After all, this is a generic binding... Hi Peter, For our needs, this is enough: the purpose of the filters is to avoid noise on the lines, the noise is as big as it is for the digital and for the analog filters, since we use an absolute measurement for them. So I do not know how useful it would be to make a difference. Wolfram, what do you think ? Eugen > > Cheers, > Peter > >> + in nanoseconds. >> + >> - interrupts >> interrupts used by the device. >> >> > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > >
Eugen, On 02/09/2019 14:15:14+0000, Eugen.Hristev@microchip.com wrote: > On 02.09.2019 13:49, Peter Rosin wrote: > > > On 2019-09-02 12:12, Eugen.Hristev@microchip.com wrote: > >> From: Eugen Hristev <eugen.hristev@microchip.com> > >> > >> Some i2c controllers have a built-in digital or analog filter. > >> This is specifically required depending on the hardware PCB/board. > >> Some controllers also allow specifying the maximum width of the > >> spikes that can be filtered. The width length can be specified in nanoseconds. > >> > >> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com> > >> --- > >> Documentation/devicetree/bindings/i2c/i2c.txt | 11 +++++++++++ > >> 1 file changed, 11 insertions(+) > >> > >> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt > >> index 44efafd..8dbff67 100644 > >> --- a/Documentation/devicetree/bindings/i2c/i2c.txt > >> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt > >> @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below. > >> Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C > >> specification. > >> > >> +- i2c-analog-filter > >> + Enable analog filter for i2c lines. > >> + > >> +- i2c-digital-filter > >> + Enable digital filter for i2c lines. > >> + > >> +- i2c-filter-width-ns > >> + Width of spikes which can be filtered by either digital or analog > >> + filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified > > > > filtr -> filter (two instances) > > > > What if you want/need to have different bandwidth for the digital and analog > > filters? After all, this is a generic binding... > > For our needs, this is enough: the purpose of the filters is to avoid > noise on the lines, the noise is as big as it is for the digital and for > the analog filters, since we use an absolute measurement for them. So I > do not know how useful it would be to make a difference. > You are adding generic properties so they have to be generic and not tied to your particular use case.
On 2019-09-02 16:15, Eugen.Hristev@microchip.com wrote: > > > On 02.09.2019 13:49, Peter Rosin wrote: > >> On 2019-09-02 12:12, Eugen.Hristev@microchip.com wrote: >>> From: Eugen Hristev <eugen.hristev@microchip.com> >>> >>> Some i2c controllers have a built-in digital or analog filter. >>> This is specifically required depending on the hardware PCB/board. >>> Some controllers also allow specifying the maximum width of the >>> spikes that can be filtered. The width length can be specified in nanoseconds. >>> >>> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com> >>> --- >>> Documentation/devicetree/bindings/i2c/i2c.txt | 11 +++++++++++ >>> 1 file changed, 11 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt >>> index 44efafd..8dbff67 100644 >>> --- a/Documentation/devicetree/bindings/i2c/i2c.txt >>> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt >>> @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below. >>> Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C >>> specification. >>> >>> +- i2c-analog-filter >>> + Enable analog filter for i2c lines. >>> + >>> +- i2c-digital-filter >>> + Enable digital filter for i2c lines. >>> + >>> +- i2c-filter-width-ns >>> + Width of spikes which can be filtered by either digital or analog >>> + filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified >> >> filtr -> filter (two instances) >> >> What if you want/need to have different bandwidth for the digital and analog >> filters? After all, this is a generic binding... > > Hi Peter, > > For our needs, this is enough: the purpose of the filters is to avoid > noise on the lines, the noise is as big as it is for the digital and for > the analog filters, since we use an absolute measurement for them. So I > do not know how useful it would be to make a difference. I think my gripe is that the description also seems non-generic. Analog filters never (ok, usually, but I have a hard time seeing how a simple analog filter can) work in terms of some "width of spikes". That phrasing seems like something inherent to trivial digital filters. For analog filters, specifying the bandwidth or cut-off frequency seems much more appropriate. And bandwidth would work equally well for digital filters, methinks. I also think it should be mentioned explicitly that this binding is for LP filters. I don't think anything else would be useful, but better safe than sorry... Hmm, would it be good or bad to specify the bandwidth relative to the current maximum bus speed? Cheers, Peter > Wolfram, what do you think ? > > Eugen > > >> >> Cheers, >> Peter >> >>> + in nanoseconds. >>> + >>> - interrupts >>> interrupts used by the device. >>> >>> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >> >>
Hi Eugen,
> Wolfram, what do you think ?
Yes, the bindings should be generic. Peter's reasoning makes much sense
to me. I am quite sure if the two of you can work things out, I'll have
nothing to add.
Thanks,
Wolfram
diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt index 44efafd..8dbff67 100644 --- a/Documentation/devicetree/bindings/i2c/i2c.txt +++ b/Documentation/devicetree/bindings/i2c/i2c.txt @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below. Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C specification. +- i2c-analog-filter + Enable analog filter for i2c lines. + +- i2c-digital-filter + Enable digital filter for i2c lines. + +- i2c-filter-width-ns + Width of spikes which can be filtered by either digital or analog + filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified + in nanoseconds. + - interrupts interrupts used by the device.