[PATCH v2 5/7] i2c: omap: wait for transfer completion before sending STP bit

Felipe Balbi balbi at ti.com
Thu Oct 25 10:15:55 EDT 2012


On Thu, Oct 25, 2012 at 06:31:58PM +0530, Santosh Shilimkar wrote:
> On Thursday 25 October 2012 05:55 PM, Felipe Balbi wrote:
> >Later patches will come adding support for
> >reporting amount of bytes transferred so that
> >client drivers can count how many bytes are
> >left to transfer.
> >
> >This is useful mostly in case of NACKs when
> >client driver wants to know exactly which
> >byte got NACKed so it doesn't have to resend
> >all bytes again.
> >
> >In order to make that work with OMAP's I2C
> >controller, we need to prevent sending STP
> >bit until message is transferred. The reason
> >behind that is because OMAP_I2C_CNT_REG gets
> >reset to original value after STP bit is
> >shifted through I2C_SDA line and that would
> >prevent us from reading the correct number of
> >bytes left to transfer.
> >
> >The full programming model suggested by IP
> >owner was the following:
> >
> >- start I2C transfer (without STP bit)
> >- upon completion or NACK, read I2C_CNT register
> >- write STP bit to I2C_CON register
> >- wait for ARDY bit
> >
> >With this patch we're implementing all steps
> >except step #2 which will come in a later
> >patch adding such support.
> >
> Will this not break the bisect since CNT and
> NACK, completion is added in later patch

not really. It keeps current behavior.

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