From mboxrd@z Thu Jan 1 00:00:00 1970 From: leilk liu Subject: Re: [PATCH v2 2/4] dt-bindings: ARM: Mediatek: Document devicetree bindings for spi bus Date: Thu, 2 Jul 2015 15:43:42 +0800 Message-ID: <1435823022.7819.8.camel@mhfsdcap03> References: <1435583070-9600-1-git-send-email-leilk.liu@mediatek.com> <1435583070-9600-3-git-send-email-leilk.liu@mediatek.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+glpam-linux-mediatek=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Daniel Kurtz Cc: Mark Rutland , "open list:OPEN FIRMWARE AND..." , Sascha Hauer , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mark Brown , linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Matthias Brugger , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: devicetree@vger.kernel.org > > + > > +- pad-select: should specify spi pad used, only required for MT8173. > > + This value should be 0~3. > > + > > +Example: > > + > > +- SoC Specific Portion: > > +spi: spi@1100a000 { > > + compatible = "mediatek,mt8173-spi"; > > + reg = <0 0x1100a000 0 0x1000>; > > + interrupts = ; > > + clocks = <&pericfg PERI_SPI0>; > > CLK_PERI_SPI0 yes,it will be fixed. > > > + clock-names = "main"; > > + pad-select = <1>; > > According to [0], a SPI bus should also specify > address-cells/size-cells to allow SPI bus devices to specify a chip > select. > [0] Documentation/devicetree/bindings/spi/spi-bus.txt > > - #address-cells - number of cells required to define a chip select > address on the SPI bus. > - #size-cells - should be zero. > > The spi-bus document even describes how to mix "native" and gpio CS lines. > Got it, it will be added in mt8173.dtsi. > > I am still not sure what to do with the "pad-select" feature. > Does "pad-select" just select one of 4 dedicated chip select lines? > Or, does it also change which CK/MOSI/MISO lines are used? > > Ideally, the same CK/MOSI/MISO signals are sent on all CK/MOSI/MISO > lines enabled by pinctrl, and "pad-select" just chooses which CS_N > line to use. > In this case, we can use the SPI slave device reg value to select > which CS_N to use for any given device. > Furthermore, we can also support using additional cs-gpios. > > However, if the pad-select also specifies which CK/MOSI/MISO pins are > used for a given transaction, then supporting cs-gpios becomes a bit > trickier, since the spi slave device would need to specify both which > gpio-cs to use, as well as which SPI pad it is connected to. > > -Dan The pad-select changes CS/CK/MO/MI lines. Mt8173 spi has 4 group pins, and it can select which group pins will be used. Leilk. > > + status = "disabled"; > > +}; > > -- > > 1.8.1.1.dirty > > > > > > _______________________________________________ > > Linux-mediatek mailing list > > Linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org > > http://lists.infradead.org/mailman/listinfo/linux-mediatek