From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Subject: [PATCH 4/4] spi: sh-msiof: Document hardware limitations related to chip selects Date: Wed, 13 Dec 2017 20:05:13 +0100 Message-ID: <1513191913-10612-5-git-send-email-geert+renesas@glider.be> References: <1513191913-10612-1-git-send-email-geert+renesas@glider.be> Cc: linux-spi@vger.kernel.org, devicetree@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Geert Uytterhoeven To: Mark Brown , Rob Herring , Mark Rutland Return-path: In-Reply-To: <1513191913-10612-1-git-send-email-geert+renesas@glider.be> Sender: linux-renesas-soc-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org Guide users to maintain the proper balance between native and GPIO chip selects. Signed-off-by: Geert Uytterhoeven --- Documentation/devicetree/bindings/spi/sh-msiof.txt | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/Documentation/devicetree/bindings/spi/sh-msiof.txt b/Documentation/devicetree/bindings/spi/sh-msiof.txt index bc8c16a6cfc82685..80710f0f04489174 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. -- 2.7.4