From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek Vasut Subject: Re: [PATCH v2 2/5] Documentation: mtd: add a DT property to set the number of dummy cycles Date: Wed, 22 Jul 2015 15:43:54 +0200 Message-ID: <201507221543.54761.marex@denx.de> References: <8119e3b46b91e43c10466b2400c6938a113b1c02.1437569902.git.cyrille.pitchen@atmel.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <8119e3b46b91e43c10466b2400c6938a113b1c02.1437569902.git.cyrille.pitchen-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Cyrille Pitchen Cc: nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org, broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, zajec5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, beanhuo-AL4WhLSQfzjQT0dZR+AlfA@public.gmane.org, juhosg-p3rKhJxN3npAfugRpC6u6w@public.gmane.org, shijie.huang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, ben-/+tVBieCtBitmTQ+vhA3Yw@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, pawel.moll-5wv7dgnIgG8@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org, galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: devicetree@vger.kernel.org On Wednesday, July 22, 2015 at 03:17:07 PM, Cyrille Pitchen wrote: > Depending on the SPI clock frequency, the Fast Read op code and the > Single/Dual Data Rate mode, the number of dummy cycles can be tuned to > improve transfer speed. > The actual number of dummy cycles is specific for each memory model and is > provided by the manufacturer thanks to the memory datasheet. > > Signed-off-by: Cyrille Pitchen > --- > Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt index > 2bee68103b01..4387567d8024 100644 > --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > @@ -19,6 +19,11 @@ Optional properties: > all chips and support for it can not be detected at > runtime. Refer to your chips' datasheet to check if this is supported by > your chip. > +- m25p,num-dummy-cycles : Set the number of dummy cycles for Fast Read > commands. + Depending on the manufacturer > additional dedicated + commands are sent to the > flash memory so the + controller and the memory > can agree on the number of + dummy cycles to use. Can't you just try negotiating this value at probe time, starting with some high value and see how low you can get with the negotiations ? This way, you'd be able to effectively auto-detect this value at probe-time. I might be wrong though :) Best regards, Marek Vasut -- 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