From: Geert Uytterhoeven <geert+renesas@glider.be>
To: Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>
Cc: linux-spi@vger.kernel.org, devicetree@vger.kernel.org,
linux-renesas-soc@vger.kernel.org,
Geert Uytterhoeven <geert+renesas@glider.be>
Subject: [PATCH 4/4] spi: sh-msiof: Document hardware limitations related to chip selects
Date: Wed, 13 Dec 2017 20:05:13 +0100 [thread overview]
Message-ID: <1513191913-10612-5-git-send-email-geert+renesas@glider.be> (raw)
In-Reply-To: <1513191913-10612-1-git-send-email-geert+renesas@glider.be>
Guide users to maintain the proper balance between native and GPIO chip
selects.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
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
next prev parent reply other threads:[~2017-12-13 19:05 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-13 19:05 [PATCH 0/4] spi: sh-msiof: Multi-slave enhancements Geert Uytterhoeven
2017-12-13 19:05 ` [PATCH 1/4] spi: sh-msiof: Avoid writing to registers from spi_master.setup() Geert Uytterhoeven
2017-12-14 11:50 ` Applied "spi: sh-msiof: Avoid writing to registers from spi_master.setup()" to the spi tree Mark Brown
[not found] ` <1513191913-10612-1-git-send-email-geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
2017-12-13 19:05 ` [PATCH 2/4] spi: sh-msiof: Extend support to 3 native chip selects Geert Uytterhoeven
2017-12-14 11:50 ` Applied "spi: sh-msiof: Extend support to 3 native chip selects" to the spi tree Mark Brown
2017-12-13 19:05 ` [PATCH 3/4] spi: sh-msiof: Implement cs-gpios configuration Geert Uytterhoeven
2017-12-14 11:49 ` Applied "spi: sh-msiof: Implement cs-gpios configuration" to the spi tree Mark Brown
2017-12-13 19:05 ` Geert Uytterhoeven [this message]
[not found] ` <1513191913-10612-5-git-send-email-geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
2017-12-14 11:45 ` [PATCH 4/4] spi: sh-msiof: Document hardware limitations related to chip selects Mark Brown
2017-12-14 11:49 ` Applied "spi: sh-msiof: Document hardware limitations related to chip selects" to the spi tree Mark Brown
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