From: Greg Ungerer <gerg-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> To: "Geert Uytterhoeven" <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>, "Uwe Kleine-König" <u.kleine-koenig-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> Cc: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>, linux-spi <linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Vladimir Zapolskiy <vladimir_zapolskiy-nmGgyN9QBj3QT0dZR+AlfA@public.gmane.org>, Sascha Hauer <kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>, Fabio Estevam <fabio.estevam-3arQi8VN3Tc@public.gmane.org>, Shawn Guo <shawnguo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org> Subject: Re: [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree Date: Wed, 22 Mar 2017 10:50:44 +1000 [thread overview] Message-ID: <51a48190-9edb-093e-a6fc-a7cb8c1e0ce0@linux-m68k.org> (raw) In-Reply-To: <CAMuHMdW+KcPCAweneu4pTg1Pb-uAvYGz1+Z=oEDYoOt4gWrjhA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> Hi Geert, Uwe, On 22/03/17 06:15, Geert Uytterhoeven wrote: > On Tue, Mar 21, 2017 at 8:23 PM, Uwe Kleine-König > <u.kleine-koenig-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> wrote: >> On Tue, Mar 21, 2017 at 11:22:27PM +1000, Greg Ungerer wrote: >>> On 21/03/17 22:11, Uwe Kleine-König wrote: >>>> On Tue, Mar 21, 2017 at 09:53:52PM +1000, Greg Ungerer wrote: >>>>> On 21/03/17 18:05, Uwe Kleine-König 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. >>>> >>>> That should be doable with gpio-cs, too. You just need the right flags >>>> in your spi transfer IIRC. >>> >>> Do you know which flag(s) do that? >> >> Looking at the source it's not about flags, but you have to split your >> transfer into several messages. > > ... and set spi_transfer.cs_change. Yep, that looks like the one. Though it would appear not all spi drivers support it. The spi-imx driver for one doesn't look at it at all. >> AFAICT that's how the spi stuff is >> supposed to work. That is, at the start of a message CS is asserted and >> (only) at it's end CS is deasserted. So the imx core with native chip >> select actually misbehaves by toggling CS between each word. > > Indeed. If you look around the kernel source for cs_change there is a number of devices that use it. A bunch od ADC/DACs in particular (including in backlight support). So I don't know that I would characterize the iMX one as misbehaving so much as only natively supporting the model where chip select is asserted/deasserted per burst. It is strait forward to implement the GPIO method instead of the native chip select with the iMX pin multiplexing. Regards Greg -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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From: gerg@linux-m68k.org (Greg Ungerer) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree Date: Wed, 22 Mar 2017 10:50:44 +1000 [thread overview] Message-ID: <51a48190-9edb-093e-a6fc-a7cb8c1e0ce0@linux-m68k.org> (raw) In-Reply-To: <CAMuHMdW+KcPCAweneu4pTg1Pb-uAvYGz1+Z=oEDYoOt4gWrjhA@mail.gmail.com> Hi Geert, Uwe, On 22/03/17 06:15, Geert Uytterhoeven wrote: > On Tue, Mar 21, 2017 at 8:23 PM, Uwe Kleine-K?nig > <u.kleine-koenig@pengutronix.de> wrote: >> On Tue, Mar 21, 2017 at 11:22:27PM +1000, Greg Ungerer wrote: >>> On 21/03/17 22:11, Uwe Kleine-K?nig wrote: >>>> On Tue, Mar 21, 2017 at 09:53:52PM +1000, Greg Ungerer wrote: >>>>> 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. >>>> >>>> That should be doable with gpio-cs, too. You just need the right flags >>>> in your spi transfer IIRC. >>> >>> Do you know which flag(s) do that? >> >> Looking at the source it's not about flags, but you have to split your >> transfer into several messages. > > ... and set spi_transfer.cs_change. Yep, that looks like the one. Though it would appear not all spi drivers support it. The spi-imx driver for one doesn't look at it at all. >> AFAICT that's how the spi stuff is >> supposed to work. That is, at the start of a message CS is asserted and >> (only) at it's end CS is deasserted. So the imx core with native chip >> select actually misbehaves by toggling CS between each word. > > Indeed. If you look around the kernel source for cs_change there is a number of devices that use it. A bunch od ADC/DACs in particular (including in backlight support). So I don't know that I would characterize the iMX one as misbehaving so much as only natively supporting the model where chip select is asserted/deasserted per burst. It is strait forward to implement the GPIO method instead of the native chip select with the iMX pin multiplexing. Regards Greg
next prev parent reply other threads:[~2017-03-22 0:50 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-17 5:03 [PATCH 0/2] spi: imx: native chip selects and devicetree Greg Ungerer 2017-03-17 5:03 ` Greg Ungerer 2017-03-17 5:03 ` [PATCH 1/2] spi: imx: set correct chip_select in platform setup Greg Ungerer 2017-03-17 5:03 ` Greg Ungerer [not found] ` <1489726983-17706-2-git-send-email-gerg-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-20 7:38 ` Shawn Guo 2017-03-20 7:38 ` Shawn Guo 2017-03-20 11:52 ` Greg Ungerer 2017-03-20 11:52 ` Greg Ungerer [not found] ` <1489726983-17706-1-git-send-email-gerg-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-17 5:03 ` [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree Greg Ungerer 2017-03-17 5:03 ` Greg Ungerer 2017-03-20 7:39 ` Shawn Guo 2017-03-20 7:39 ` Shawn Guo [not found] ` <1489726983-17706-3-git-send-email-gerg-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-20 13:22 ` Vladimir Zapolskiy 2017-03-20 13:22 ` Vladimir Zapolskiy 2017-03-21 2:05 ` Greg Ungerer 2017-03-21 2:05 ` Greg Ungerer [not found] ` <4a8449d9-cc38-d642-0853-246f46ee7059-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-21 8:05 ` Uwe Kleine-König 2017-03-21 8:05 ` Uwe Kleine-König 2017-03-21 11:53 ` Greg Ungerer 2017-03-21 11:53 ` Greg Ungerer [not found] ` <942cfc4b-445b-ca51-1823-2391cea62abf-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-21 12:11 ` Uwe Kleine-König 2017-03-21 12:11 ` Uwe Kleine-König [not found] ` <20170321121133.jcmhhbszj2d42h3w-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> 2017-03-21 13:22 ` Greg Ungerer 2017-03-21 13:22 ` Greg Ungerer [not found] ` <20678cef-f667-9915-aa00-8877ad152a8c-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-03-21 19:23 ` Uwe Kleine-König 2017-03-21 19:23 ` Uwe Kleine-König 2017-03-21 20:15 ` Geert Uytterhoeven 2017-03-21 20:15 ` Geert Uytterhoeven [not found] ` <CAMuHMdW+KcPCAweneu4pTg1Pb-uAvYGz1+Z=oEDYoOt4gWrjhA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2017-03-22 0:50 ` Greg Ungerer [this message] 2017-03-22 0:50 ` Greg Ungerer 2017-03-22 7:09 ` Geert Uytterhoeven 2017-03-22 7:09 ` Geert Uytterhoeven 2017-09-04 12:47 ` Applied "spi: imx: fix use of native chip-selects with devicetree" to the spi tree Mark Brown 2017-09-04 12:47 ` Mark Brown 2017-10-10 20:38 ` [2/2] spi: imx: fix use of native chip-selects with devicetree Trent Piepho 2017-10-10 20:38 ` Trent Piepho 2017-10-12 6:26 ` Greg Ungerer 2017-10-12 6:26 ` Greg Ungerer [not found] ` <209bb901-875e-8007-06f8-3ae9698a0e41-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org> 2017-10-12 20:41 ` Trent Piepho 2017-10-12 20:41 ` Trent Piepho 2017-03-20 7:35 ` [PATCH 0/2] spi: imx: native chip selects and devicetree Shawn Guo 2017-03-20 7:35 ` Shawn Guo
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