On 11/19/2013 3:42 AM, Thierry Reding wrote: > * PGP Signed by an unknown key > > On Mon, Nov 18, 2013 at 11:48:10AM +0000, Mark Rutland wrote: >> On Mon, Nov 18, 2013 at 10:30:47AM +0000, Thierry Reding wrote: >>> From: Rhyland Klein <rkl...@nvidia.com> >>> >>> The EC has specific timing it requires. Add support for an optional delay >>> after raising CS to fix timing issues. This is configurable based on >>> a DT property "google,cros-ec-spi-msg-delay". >>> >>> If this property isn't set, then no delay will be added. However, if set >>> it will cause a delay equal to the value passed to it to be inserted at >>> the end of a transaction. >>> >>> Signed-off-by: Rhyland Klein <rkl...@nvidia.com> >>> Reviewed-by: Bernie Thompson <bhthomp...@chromium.org> >>> Reviewed-by: Andrew Bresticker <abres...@chromium.org> >>> Cc: Rob Herring <rob.herr...@calxeda.com> >>> Cc: Pawel Moll <pawel.m...@arm.com> >>> Cc: Mark Rutland <mark.rutl...@arm.com> >>> Cc: Ian Campbell <ijc+devicet...@hellion.org.uk> >>> Signed-off-by: Thierry Reding <tred...@nvidia.com> >>> --- >>> Documentation/devicetree/bindings/mfd/cros-ec.txt | 4 +++ >>> drivers/mfd/cros_ec_spi.c | 30 >>> +++++++++++++++++++++++ >>> 2 files changed, 34 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/mfd/cros-ec.txt >>> b/Documentation/devicetree/bindings/mfd/cros-ec.txt >>> index 5f229c5f6da9..fb3034a87ae0 100644 >>> --- a/Documentation/devicetree/bindings/mfd/cros-ec.txt >>> +++ b/Documentation/devicetree/bindings/mfd/cros-ec.txt >>> @@ -17,6 +17,10 @@ Required properties (SPI): >>> - compatible: "google,cros-ec-spi" >>> - reg: SPI chip select >>> >>> +Optional properties (SPI): >>> +- google,cros-ec-spi-msg-delay: This property is how long of a delay, in >>> usecs, >>> + to use on the last transfer of a message, to force time between >>> transactions. >>> + >> >> Lose the "This property is", that's obvious from the structure of the >> document. > > Will do. > >> It would be nice to have an explanation in the binding document as to >> _why_ you might want to do this (e.g. the HW expects the rising edge to >> come some number of uS after the data, if it comes too early it >> explodes). > > From what I can tell, this might differ on the exact variant of the EC, > but generally it seems that when the interval between two transactions > isn't long enough the EC won't be able to respond properly in time and > cause subsequent transactions to hang. Perhaps Rhyland, Bernie or Andrew > are more familiar with the details and therefore can provide a better or > more accurate explanation.
I believe this explanation is correct. As I recall, I think adding this delay helped stabilize communication with the EC, where before sometimes transactions would time out. -rhyland > >> Otherwise this looks fine to me. > > Thanks, > Thierry > > * Unknown Key > * 0x7F3EB3A1 > -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
