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From: Rob Herring <robh@kernel.org>
To: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Cc: Brendan Higgins <brendanhiggins@google.com>,
	Wolfram Sang <wsa@the-dreams.de>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Joel Stanley <joel@jms.id.au>,
	Mark Rutland <mark.rutland@arm.com>,
	Andrew Jeffery <andrew@aj.id.au>, Tao Ren <taoren@fb.com>,
	Cedric Le Goater <clg@kaod.org>,
	Linux I2C <linux-i2c@vger.kernel.org>,
	devicetree@vger.kernel.org,
	linux-aspeed <linux-aspeed@lists.ozlabs.org>,
	OpenBMC Maillist <openbmc@lists.ozlabs.org>
Subject: Re: [PATCH v4 1/4] dt-bindings: i2c: aspeed: add transfer mode support
Date: Tue, 9 Mar 2021 19:15:34 -0700
Message-ID: <CAL_Jsq+H2wCyTKhGcQvgiuyMtGW0hytQgw=948q0JGLSLOo9KA@mail.gmail.com> (raw)
In-Reply-To: <f6732348-d6c8-f49b-6123-afe542bb1f8c@linux.intel.com>

On Tue, Mar 9, 2021 at 10:02 AM Jae Hyun Yoo
<jae.hyun.yoo@linux.intel.com> wrote:
>
> Hi Rob,
>
> On 3/6/2021 12:30 PM, Rob Herring wrote:
> > On Wed, Feb 24, 2021 at 11:17:17AM -0800, Jae Hyun Yoo wrote:
> >> Append bindings to support transfer mode.
> >>
> >> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> >> Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
> >> ---
> >> Changes since v3:
> >> - None
> >>
> >> Changes since v2:
> >> - Moved SRAM resources back to default dtsi and added mode selection
> >>    property.
> >>
> >> Changes since v1:
> >> - Removed buffer reg settings from default device tree and added the settings
> >>    into here to show the predefined buffer range per each bus.
> >>
> >>   .../devicetree/bindings/i2c/i2c-aspeed.txt    | 37 +++++++++++++++----
> >>   1 file changed, 30 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> >> index b47f6ccb196a..242343177324 100644
> >> --- a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> >> +++ b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
> >> @@ -17,6 +17,20 @@ Optional Properties:
> >>   - bus-frequency    : frequency of the bus clock in Hz defaults to 100 kHz when not
> >>                specified
> >>   - multi-master     : states that there is another master active on this bus.
> >> +- aspeed,i2c-xfer-mode      : should be "byte", "buf" or "dma" to select transfer
> >> +                      mode defaults to "byte" mode when not specified.
> >> +
> >> +                      I2C DMA mode on AST2500 has these restrictions:
> >> +                        - If one of these controllers is enabled
> >> +                            * UHCI host controller
> >> +                            * MCTP controller
> >> +                          I2C has to use buffer mode or byte mode instead
> >> +                          since these controllers run only in DMA mode and
> >> +                          I2C is sharing the same DMA H/W with them.
> >> +                        - If one of these controllers uses DMA mode, I2C
> >> +                          can't use DMA mode
> >> +                            * SD/eMMC
> >> +                            * Port80 snoop
> >
> > How does one decide between byte or buf mode?
>
> If a given system makes just one byte r/w transactions most of the time
> then byte mode will be a right setting. Otherwise, buf mode is more
> efficient because it doesn't generate a bunch of interrupts on every
> byte handling.

Then why doesn't the driver do byte transactions when it gets small
1-4? byte transactions and buffer transactions when it gets larger
sized transactions.

Rob

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-24 19:17 [PATCH v4 0/4] i2c: aspeed: Add buffer and DMA modes support Jae Hyun Yoo
2021-02-24 19:17 ` [PATCH v4 1/4] dt-bindings: i2c: aspeed: add transfer mode support Jae Hyun Yoo
2021-03-06 20:30   ` Rob Herring
2021-03-09 17:02     ` Jae Hyun Yoo
2021-03-10  2:15       ` Rob Herring [this message]
2021-03-10 15:55         ` Jae Hyun Yoo
2021-04-08 17:50           ` Jae Hyun Yoo
2021-04-13 19:50             ` Brendan Higgins
2021-02-24 19:17 ` [PATCH v4 2/4] ARM: dts: aspeed: modify I2C node to support buffer mode Jae Hyun Yoo
2021-02-24 19:17 ` [PATCH v4 3/4] i2c: aspeed: add buffer mode transfer support Jae Hyun Yoo
2021-04-13 21:24   ` Brendan Higgins
2021-02-24 19:17 ` [PATCH v4 4/4] i2c: aspeed: add DMA " Jae Hyun Yoo
2021-04-13 21:32   ` Brendan Higgins
2021-04-14 15:08     ` Jae Hyun Yoo
2021-05-19 18:38       ` Jae Hyun Yoo

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