From mboxrd@z Thu Jan 1 00:00:00 1970 From: shawnguo@kernel.org (Shawn Guo) Date: Mon, 20 Mar 2017 15:39:38 +0800 Subject: [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree In-Reply-To: <1489726983-17706-3-git-send-email-gerg@linux-m68k.org> References: <1489726983-17706-1-git-send-email-gerg@linux-m68k.org> <1489726983-17706-3-git-send-email-gerg@linux-m68k.org> Message-ID: <20170320073937.GE3443@dragon> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Mar 17, 2017 at 03:03:03PM +1000, Greg Ungerer wrote: > The commonly used mechanism of specifying the hardware or native > chip-select on an SPI device in devicetree (that is "cs-gpios = <0>") > does not result in the native chip-select being configured for use. > So external SPI devices that require use of the native chip-select > will not work. > > You can successfully specify native chip-selects if using a platform > setup by specifying the cs-gpio as negative offset by 32. And that > works correctly. You cannot use the same method in devicetree. > > The logic in the spi-imx.c driver during probe uses core spi function > of_spi_register_master() in spi.c to parse the "cs-gpios" devicetree tag. > For valid GPIO values that will be recorded for use, all other entries in > the cs_gpios list will be set to -ENOENT. So entries like "<0>" will be > set to -ENOENT in the cs_gpios list. > > When the SPI device registers are setup the code will use the GPIO > listed in the cs_gpios list for the desired chip-select. If the cs_gpio > is less then 0 then it is intended to be for a native chip-select, and > its cs_gpio value is added to 32 to get the chipselect number to use. > Problem is that with devicetree this can only ever be -ENOENT (which > is -2), and that alone results in an invalid chip-select number. But also > doesn't allow selection of the native chip-select at all. > > To fix, if the cs_gpio specified for this spi device is not a > valid GPIO then use the "chip_select" (that is the native chip-select > number) for hardware setup. > > Signed-off-by: Greg Ungerer Acked-by: Shawn Guo