On Tue, Mar 9, 2021 at 10:02 AM Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> > >> Reviewed-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx> > >> --- > >> 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
