From: Geert Uytterhoeven <geert@linux-m68k.org> To: Greg Ungerer <gerg@linux-m68k.org> Cc: "Sascha Hauer" <s.hauer@pengutronix.de>, linux-spi <linux-spi@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "Sascha Hauer" <kernel@pengutronix.de>, "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>, "Fabio Estevam" <fabio.estevam@nxp.com>, "Shawn Guo" <shawnguo@kernel.org>, "Vladimir Zapolskiy" <vladimir_zapolskiy@mentor.com> Subject: Re: [PATCH 2/2] spi: imx: fix use of native chip-selects with devicetree Date: Wed, 22 Mar 2017 08:09:35 +0100 [thread overview] Message-ID: <CAMuHMdW+sqSyoQUE7sGPKoXy7n9Bh2QGg5BNA1EP5=eW4GKTVA@mail.gmail.com> (raw) In-Reply-To: <51a48190-9edb-093e-a6fc-a7cb8c1e0ce0@linux-m68k.org> Hi Greg, On Wed, Mar 22, 2017 at 1:50 AM, Greg Ungerer <gerg@linux-m68k.org> wrote: > On 22/03/17 06:15, Geert Uytterhoeven wrote: >> On Tue, Mar 21, 2017 at 8:23 PM, Uwe Kleine-König >> <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-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. Correct. With many drivers, you must use cs-gpios to support that feature. Remember, SPI is a mixed bag of features, and not all of them are supported on all controllers. >>> 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. It's up to the system integrator to specify cs-gpios when needed. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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From: geert@linux-m68k.org (Geert Uytterhoeven) 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 08:09:35 +0100 [thread overview] Message-ID: <CAMuHMdW+sqSyoQUE7sGPKoXy7n9Bh2QGg5BNA1EP5=eW4GKTVA@mail.gmail.com> (raw) In-Reply-To: <51a48190-9edb-093e-a6fc-a7cb8c1e0ce0@linux-m68k.org> Hi Greg, On Wed, Mar 22, 2017 at 1:50 AM, Greg Ungerer <gerg@linux-m68k.org> wrote: > 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. Correct. With many drivers, you must use cs-gpios to support that feature. Remember, SPI is a mixed bag of features, and not all of them are supported on all controllers. >>> 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. It's up to the system integrator to specify cs-gpios when needed. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
next prev parent reply other threads:[~2017-03-22 7:09 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 2017-03-22 0:50 ` Greg Ungerer 2017-03-22 7:09 ` Geert Uytterhoeven [this message] 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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