i2c: document the SDA hold time binding

Message ID 20190211132515.24163-1-wsa+renesas@sang-engineering.com
State New
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Series
  • i2c: document the SDA hold time binding
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Commit Message

Wolfram Sang Feb. 11, 2019, 1:25 p.m.
The documentation was forgotten when the feature was added.

Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---

To everyone on CC: I want to confirm here that you use the value really for
t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...

 Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Andy Shevchenko Feb. 11, 2019, 2:40 p.m. | #1
On Mon, Feb 11, 2019 at 02:25:15PM +0100, Wolfram Sang wrote:
> The documentation was forgotten when the feature was added.
> 
> Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
> 
> To everyone on CC: I want to confirm here that you use the value really for
> t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...

+Cc: Jarkko

> 
>  Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index 44efafdfd7f5..b7bc4c4cc2e6 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -55,6 +55,10 @@ 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-sda-hold-time-ns
> +	Number of nanoseconds the SDA signal needs to be held; t(hd:sta) in
> +	the I2C specification.
> +
>  - interrupts
>  	interrupts used by the device.
>  
> -- 
> 2.11.0
>
Ludovic Desroches Feb. 13, 2019, 10:24 a.m. | #2
Hi Wolfram,

On Mon, Feb 11, 2019 at 02:25:15PM +0100, Wolfram Sang wrote:
> The documentation was forgotten when the feature was added.
> 
> Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
> 
> To everyone on CC: I want to confirm here that you use the value really for
> t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...


No in our case, it's t(hd:dat):
TWD is kept unchanged after TWCK falling edge for a
period of (HOLD + 3) × t peripheral clock


Ludovic

> 
>  Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index 44efafdfd7f5..b7bc4c4cc2e6 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -55,6 +55,10 @@ 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-sda-hold-time-ns
> +	Number of nanoseconds the SDA signal needs to be held; t(hd:sta) in
> +	the I2C specification.
> +
>  - interrupts
>  	interrupts used by the device.
>  
> -- 
> 2.11.0
>
Ludovic Desroches Feb. 13, 2019, 10:27 a.m. | #3
Sorry I didn't keep the addition of Jarkko to the CC list.

On Wed, Feb 13, 2019 at 11:24:37AM +0100, Ludovic Desroches wrote:
> Hi Wolfram,
> 
> On Mon, Feb 11, 2019 at 02:25:15PM +0100, Wolfram Sang wrote:
> > The documentation was forgotten when the feature was added.
> > 
> > Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
> > Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> > ---
> > 
> > To everyone on CC: I want to confirm here that you use the value really for
> > t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...
> 
> 
> No in our case, it's t(hd:dat):
> TWD is kept unchanged after TWCK falling edge for a
> period of (HOLD + 3) × t peripheral clock
> 
> 
> Ludovic
> 
> > 
> >  Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> > index 44efafdfd7f5..b7bc4c4cc2e6 100644
> > --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> > +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> > @@ -55,6 +55,10 @@ 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-sda-hold-time-ns
> > +	Number of nanoseconds the SDA signal needs to be held; t(hd:sta) in
> > +	the I2C specification.
> > +
> >  - interrupts
> >  	interrupts used by the device.
> >  
> > -- 
> > 2.11.0
> >
Andy Shevchenko March 18, 2019, 10:35 a.m. | #4
On Mon, Feb 11, 2019 at 02:25:15PM +0100, Wolfram Sang wrote:
> The documentation was forgotten when the feature was added.
> 
> Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
> 
> To everyone on CC: I want to confirm here that you use the value really for
> t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...

I guess in our case it's also t(hd:dat).

Jarkko?

> 
>  Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index 44efafdfd7f5..b7bc4c4cc2e6 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -55,6 +55,10 @@ 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-sda-hold-time-ns
> +	Number of nanoseconds the SDA signal needs to be held; t(hd:sta) in
> +	the I2C specification.
> +
>  - interrupts
>  	interrupts used by the device.
>  
> -- 
> 2.11.0
>
Jarkko Nikula March 18, 2019, 11:22 a.m. | #5
On 3/18/19 12:35 PM, Andy Shevchenko wrote:
> On Mon, Feb 11, 2019 at 02:25:15PM +0100, Wolfram Sang wrote:
>> The documentation was forgotten when the feature was added.
>>
>> Fixes: 4717be73c284 ("i2c: core: Parse SDA hold time from firmware")
>> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
>> ---
>>
>> To everyone on CC: I want to confirm here that you use the value really for
>> t(hd:sta) and not t(hd:dat). I'd be a little confused otherwise...
> 
> I guess in our case it's also t(hd:dat).
> 
The DesignWare specification I have mention only tHD;DAT.

Patch

diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
index 44efafdfd7f5..b7bc4c4cc2e6 100644
--- a/Documentation/devicetree/bindings/i2c/i2c.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c.txt
@@ -55,6 +55,10 @@  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-sda-hold-time-ns
+	Number of nanoseconds the SDA signal needs to be held; t(hd:sta) in
+	the I2C specification.
+
 - interrupts
 	interrupts used by the device.