Re: [PATCH 1/5] spi: do not fail if the CS line is not connected

From	Andi Shyti <andi@etezian.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/5] spi: do not fail if the CS line is not connected
Date	2016-06-19 08:10 +0200
Message-ID	<rLE5H-6LL-1@gated-at.bofh.it> (permalink)
References	<rKWR3-3Hd-11@gated-at.bofh.it> <rKX0L-3ZY-37@gated-at.bofh.it> <rKZvz-5q4-3@gated-at.bofh.it> <rL0rE-60E-19@gated-at.bofh.it> <rL14l-6sY-5@gated-at.bofh.it>
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Hi Mark,

> > > > In this case do not fail and defer to the SPI device drivers the
> > > > responsibility to check whether the num-cs is '0'.
> 
> > > A SPI controller always has one chip seelct, it may not be controllable
> > > but it's at least logically present.
> 
> > This is true, but there are cases where the CS is not connected
> > and this case needs to be treated separately to allow the device
> > to work.
> 
> In what way?  It is just as easy for a device with no physical chip
> select to have a logical chip select of 0 that it does nothing with as
> it is for that device to handle any other number.

That is indeed my case: the s3c64xx doesn't send anything, unless
I manually enable CS (from the next patches I need to write '0'
in the CS register). But I need smoething to tell to the
device that the CS line is not connected, for example a flag in
the DTS.

It comes natural to me to set "num-cs = <0>" instead of defining
a new property. In this case I will consider that there is no CS
line, even though there is a CS controller.

Thanks,
Andi

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[PATCH 0/5] SPI CS line logical change and s3c64xx code rework Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:00 +0200
  [PATCH 5/5] spi: s3c63xx: simplify if statement in prepare_transfer  function Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:10 +0200
  [PATCH 2/5] spi: s3c64xx: group the CS signalling writes in a single  function Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:10 +0200
  [PATCH 4/5] spi: s3c64xx: do not configure the device twice Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:10 +0200
  [PATCH 3/5] spi: s3c64xx: consider the case where the CS line is not  connected Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:10 +0200
  [PATCH 1/5] spi: do not fail if the CS line is not connected Andi Shyti <andi.shyti@samsung.com> - 2016-06-17 10:10 +0200
    Re: [PATCH 1/5] spi: do not fail if the CS line is not connected Mark Brown <broonie@kernel.org> - 2016-06-17 12:50 +0200
      Re: [PATCH 1/5] spi: do not fail if the CS line is not connected Andi Shyti <andi@etezian.org> - 2016-06-17 13:50 +0200
        Re: [PATCH 1/5] spi: do not fail if the CS line is not connected Mark Brown <broonie@kernel.org> - 2016-06-17 14:30 +0200
          Re: [PATCH 1/5] spi: do not fail if the CS line is not connected Andi Shyti <andi@etezian.org> - 2016-06-19 08:10 +0200

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