From mboxrd@z Thu Jan 1 00:00:00 1970 From: gerg@linux-m68k.org (Greg Ungerer) Date: Tue, 21 Mar 2017 21:53:52 +1000 Subject: [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree In-Reply-To: <20170321080551.ie4xm5hr3fki365s@pengutronix.de> References: <1489726983-17706-1-git-send-email-gerg@linux-m68k.org> <1489726983-17706-3-git-send-email-gerg@linux-m68k.org> <4a8449d9-cc38-d642-0853-246f46ee7059@linux-m68k.org> <20170321080551.ie4xm5hr3fki365s@pengutronix.de> Message-ID: <942cfc4b-445b-ca51-1823-2391cea62abf@linux-m68k.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 21/03/17 18:05, Uwe Kleine-K?nig wrote: > On Tue, Mar 21, 2017 at 12:05:20PM +1000, Greg Ungerer wrote: >> On 20/03/17 23:22, Vladimir Zapolskiy wrote: >>> For that type of bindings locally I have a hackish spi-imx driver change, >>> which supports this option, but I'm unsure if it is universal enough. >> >> Do you mean supporting no cs-gpios tag? >> That would be nice, but it would seem not many users of this are >> using native chip selects. > > The reason for this is that the native chip selects are less flexible > than gpios because you cannot control when they deassert. IIRC they do > it too much for some chips. So the only reason to stick to them is that > on some SoCs not all pins have a GPIO function. Not sure if transfer > speed is another reason, but I would expect that the gain isn't that > big. For the particular SPI device I am using, a Silicon Labs 32260, it actually wants the assertion and de-assertion of the chip-select between each byte. So it is the only way it can work for me. Regards Greg