Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50

From	Andrey Pronin <apronin@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50
Date	2016-07-20 21:50 +0200
Message-ID	<rX5Fh-5EF-37@gated-at.bofh.it> (permalink)
References	<rV133-14j-7@gated-at.bofh.it> <rWQGd-4wj-5@gated-at.bofh.it> <rWQGd-4wj-3@gated-at.bofh.it> <rX52x-5nW-9@gated-at.bofh.it>
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On Wed, Jul 20, 2016 at 02:03:03PM -0500, Rob Herring wrote:
> On Tue, Jul 19, 2016 at 08:41:24PM -0700, Andrey Pronin wrote:

Hi Rob,

> As I mentioned, there may be common properties. It doesn't seem you 
> looked, so I did:
> 
> - spi-rx-delay-us  - (optional) Microsecond delay after a read transfer.
> - spi-tx-delay-us  - (optional) Microsecond delay after a write transfer.
> 
> Seems to me setting one or both of these should work for you.
>

Yes, good catch, my fault I didn't see those.
But they are not exactly what I mean and need. I don't need delay after
each read or write transfer. What is needed is a guaranteed time
between transfers.

So, if the next transaction doesn't come withing the next X ms (or us),
we don't waste time on inserting a delays after this transaction at all.
Following the description and always inserting a delay must work well
for short microseconds-long delays. For longer milliseconds-long delays
a different strategy of checking the time when the previous transaction
was and only delaying if it was not too long ago is better.

Thus, I won't be able to re-use these properties anyways based on their
current description in bindings/spi/spi-bus.txt.

> > +- sleep-delay-ms: Time after the last SPI activity, after which the chip
> > +  may go to sleep.
> > +- wake-start-delay-ms: Time after initiating wake up before the chip is
> > +  ready to accept commands over SPI.
> 
> I also asked why these 2 can't be hard-coded in the driver?
>

Sorry, I just updated this patch description in v2 to indicate why they are not
hard-coded, but didn't answer explicitly. As the firmware changes, a different
revision of it can have a different time before it sleeps in its configuration,
or the time it takes it to startup may be different. Thus, there's a way to
set it here w/o changing the driver.

Andrey

Thread

[PATCH 0/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-15 04:30 +0200
  [PATCH 1/2] tpm: devicetree: document properties for cr50 Andrey Pronin <apronin@chromium.org> - 2016-07-15 04:30 +0200
    Re: [PATCH 1/2] tpm: devicetree: document properties for cr50 Guenter Roeck <groeck@google.com> - 2016-07-15 06:10 +0200
      Re: [PATCH 1/2] tpm: devicetree: document properties for cr50 Andrey Pronin <apronin@chromium.org> - 2016-07-15 19:40 +0200
        Re: [PATCH 1/2] tpm: devicetree: document properties for cr50 Guenter Roeck <groeck@google.com> - 2016-07-15 20:30 +0200
    Re: [PATCH 1/2] tpm: devicetree: document properties for cr50 Rob Herring <robh@kernel.org> - 2016-07-17 15:30 +0200
  [PATCH 2/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-15 04:30 +0200
    Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-07-15 05:40 +0200
      Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-15 05:50 +0200
        Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-07-19 15:00 +0200
          Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-20 02:30 +0200
            Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-07-20 19:10 +0200
              Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-21 20:20 +0200
                Re: [PATCH 2/2] tpm: add driver for cr50 on SPI Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-07-21 23:10 +0200
  Re: [PATCH 0/2] tpm: add driver for cr50 on SPI Peter Huewe <peterhuewe@gmx.de> - 2016-07-15 04:30 +0200
    Re: [PATCH 0/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-15 05:00 +0200
      Re: [PATCH 0/2] tpm: add driver for cr50 on SPI Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-07-15 05:30 +0200
        Re: [PATCH 0/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-15 19:20 +0200
  Re: [PATCH 0/2] tpm: add driver for cr50 on SPI Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-07-19 15:00 +0200
  [PATCH v2 1/2] tpm: devicetree: document properties for cr50 Andrey Pronin <apronin@chromium.org> - 2016-07-20 05:50 +0200
    Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50 Rob Herring <robh@kernel.org> - 2016-07-20 21:10 +0200
      Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50 Andrey Pronin <apronin@chromium.org> - 2016-07-20 21:50 +0200
        Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50 Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-07-20 22:00 +0200
        Re: [PATCH v2 1/2] tpm: devicetree: document properties for cr50 Rob Herring <robh@kernel.org> - 2016-07-21 23:10 +0200
  [PATCH v2 0/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-20 05:50 +0200
    [PATCH v2 2/2] tpm: add driver for cr50 on SPI Andrey Pronin <apronin@chromium.org> - 2016-07-20 05:50 +0200
    Aw: [PATCH v2 0/2] tpm: add driver for cr50 on SPI "Peter Huewe" <PeterHuewe@gmx.de> - 2016-07-25 19:10 +0200

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