From: Geert Uytterhoeven Date: Wed, 13 Dec 2017 19:05:13 +0000 (+0100) Subject: spi: sh-msiof: Document hardware limitations related to chip selects X-Git-Tag: v4.16-rc1~188^2~1^4 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=c99182f73cce7926c623b5c1c0ff0b7954ac8d81;p=linux.git spi: sh-msiof: Document hardware limitations related to chip selects Guide users to maintain the proper balance between native and GPIO chip selects. Signed-off-by: Geert Uytterhoeven Signed-off-by: Mark Brown --- diff --git a/Documentation/devicetree/bindings/spi/sh-msiof.txt b/Documentation/devicetree/bindings/spi/sh-msiof.txt index bc8c16a6cfc8..80710f0f0448 100644 --- a/Documentation/devicetree/bindings/spi/sh-msiof.txt +++ b/Documentation/devicetree/bindings/spi/sh-msiof.txt @@ -41,6 +41,16 @@ Optional properties: 0: MSIOF_SYNC 1: MSIOF_SS1 2: MSIOF_SS2 + Hardware limitations related to chip selects: + - Native chip selects are always deasserted in + between transfers that are part of the same + message. Use cs-gpios to work around this. + - All slaves using native chip selects must use the + same spi-cs-high configuration. Use cs-gpios to + work around this. + - When using GPIO chip selects, at least one native + chip select must be left unused, as it will be + driven anyway. - dmas : Must contain a list of two references to DMA specifiers, one for transmission, and one for reception.