linux-kernel - Re: [PATCH 1/2] dt-bindings: spi: Add Spreadtrum SPI controller documentation

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Date:   Wed, 8 Aug 2018 10:50:25 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        lanqing.liu@...eadtrum.com, linux-spi@...r.kernel.org,
        DTML <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: spi: Add Spreadtrum SPI controller
 documentation

On Wed, Aug 08, 2018 at 10:26:42AM +0800, Baolin Wang wrote:

> Sorry for confusing. Let me try to explain it explicitly.
> We can set the word size (bits_per_word) for each transmission, for
> our SPI controller,  after every word size transmission, we need one
> interval time (hardware automatically) to make sure the slave has
> enough time to receive the whole data.

OK, so it's an inter word delay.  Some other controllers definitely have
the same feature.

> Yes, I agree we should configure it at runtime by the device, but we
> did not find one member to use in 'struct spi_transfer', we just find
> one similar 'delay_usecs' member in 'struct spi_transfer' but not
> same. We can use  'delay_usecs' to set our hardware interval value,
> but we should clean it when transfer is done, since we do not need to
> delay after the transfer in spi_transfer_one _message(). Or can we add
> one new member maybe named 'word_interval' to indicate the interval
> time between word size transmission?

Right, I don't think we added this yet (if we did I can't see it).  I'd
add a new field to spi_transfer for this, then other controllers with
the same support can implement it as well and drivers can start using
it too.

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