linux-kernel - Re: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start property for Cadence I2C

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Date:	Tue, 2 Dec 2014 11:19:07 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Harini Katakam <harinik@...inx.com>
Cc:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"michal.simek@...inx.com" <michal.simek@...inx.com>,
	"soren.brinkmann@...inx.com" <soren.brinkmann@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"vishnum@...inx.com" <vishnum@...inx.com>
Subject: Re: [PATCH 3/4] devicetree: bindings: Add defeature-repeated-start
 property for Cadence I2C

On Tue, Dec 02, 2014 at 10:05:48AM +0000, Harini Katakam wrote:
> From: Vishnu Motghare <vishnum@...inx.com>
> 
> This patch adds "defeature-repeated-start" property in i2c-cadence.txt.
> 
> Signed-off-by: Vishnu Motghare <vishnum@...inx.com>
> Signed-off-by: Harini Katakam <harinik@...inx.com>
> ---
>  .../devicetree/bindings/i2c/i2c-cadence.txt        |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-cadence.txt b/Documentation/devicetree/bindings/i2c/i2c-cadence.txt
> index 7cb0b56..9d417a7 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-cadence.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-cadence.txt
> @@ -11,6 +11,17 @@ Required properties:
>  Optional properties:
>    - clock-frequency: Desired operating frequency, in Hz, of the bus.
>    - clock-names: Input clock name, should be 'pclk'.
> +  - defeature-repeated-start: Include this property to defeature repeated start
> +			      This defeature is due to a few bugs in the
> +			      I2C controller.
> +			      Completion interrupt after a read/receive
> +			      operation is NOT obtained if HOLD bit is set
> +			      at that time. Because of this bug, repeated start
> +			      will only work if there are no transfers following
> +			      a read/receive transfer.
> +			      If HOLD is held for long without a transfer,
> +			      invalid read transactions are generated by the
> +			      controller due to a HW timeout related bug.

I'm not keen on the name; it sounds like we're disabling a feature
rather than describing the problem (and "defeature" is not a common
term in this sense, "disable" would be better).

It sounds like there are two issues with staying in the HOLD state? Lost
completion IRQs and a separate HW timeout bug? Or are the two related?

Thanks,
Mark.
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