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

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Date:   Wed, 15 Aug 2018 10:17:12 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Trent Piepho <tpiepho@...inj.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "orsonzhai@...il.com" <orsonzhai@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "zhang.lyra@...il.com" <zhang.lyra@...il.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "lanqing.liu@...eadtrum.com" <lanqing.liu@...eadtrum.com>
Subject: Re: [PATCH 1/2] dt-bindings: spi: Add Spreadtrum SPI controller documentation

Hi Rob,

On 15 August 2018 at 04:27, Rob Herring <robh@...nel.org> wrote:
> On Thu, Aug 09, 2018 at 11:03:11AM +0800, Baolin Wang wrote:
>> Hi Trent,
>>
>> On 9 August 2018 at 02:57, Trent Piepho <tpiepho@...inj.com> wrote:
>> > On Wed, 2018-08-08 at 11:54 +0100, Mark Brown wrote:
>> >> On Wed, Aug 08, 2018 at 06:35:28PM +0800, Baolin Wang wrote:
>> >> > On 8 August 2018 at 17:50, Mark Brown <broonie@...nel.org> wrote:
>> >> > > 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.
>> >> > OK. So I will name the new filed as 'word_delay', is it OK for you?
>> >>
>> >> Sounds good, yes.
>> >
>> > Should it be in µs like the existing iter-transfer delay?  I think
>> > perhaps units of cycles of the SPI clock make more sense?
>>
>> Since some SPI controllers just want some interval values (neither µs
>> unit nor cycles unit ) set into hardware, and the hardware will
>> convert to the correct delay time automatically. So I did not force
>> 'word_delay' unit as µs or cycle, and just let the slave devices
>> decide the unit which depends on the SPI hardware requirement.
>
> This needs to be defined units in DT, not decided by each controller.

Do you mean we should introduce one standard property (maybe named as
'word_delay_unit') to define the word_delay unit?
If we really need to specify the unit of word_delay, I think we can
add comments for spi_tansfer  to specify the unit, which will be
better.

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index a64235e..7a72c0a 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -711,6 +711,8 @@ extern void spi_res_release(struct spi_controller *ctlr,
  * @delay_usecs: microseconds to delay after this transfer before
  * (optionally) changing the chipselect status, then starting
  * the next transfer or completing this @spi_message.
+ * @word_delay: clock cycles to inter word delay after each word size
(set by bits_per_word)
+ * transmission.
  * @transfer_list: transfers are sequenced through @spi_message.transfers
  * @tx_sg: Scatterlist for transmit, currently not for client use
  * @rx_sg: Scatterlist for receive, currently not for client use
@@ -793,6 +795,7 @@ struct spi_transfer {
  u8 bits_per_word;
  u16 delay_usecs;
  u32 speed_hz;
+ u16 word_delay;

  struct list_head transfer_list;
 };


-- 
Baolin Wang
Best Regards