From mboxrd@z Thu Jan 1 00:00:00 1970 From: Murali Karicheri Subject: Re: [PATCH v2] spi: davinci: add support for adding delay between word's transmission Date: Tue, 9 Sep 2014 13:09:27 -0400 Message-ID: <540F3447.3020609@ti.com> References: <1410278851-10783-1-git-send-email-grygorii.strashko@ti.com> <20140909165555.GD2601@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , Ian Campbell , , Rob Herring , , To: Mark Brown Return-path: In-Reply-To: <20140909165555.GD2601-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: Errors-To: davinci-linux-open-source-bounces-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org List-Id: linux-spi.vger.kernel.org On 09/09/2014 12:55 PM, Mark Brown wrote: > On Tue, Sep 09, 2014 at 07:07:31PM +0300, Grygorii Strashko wrote: > >> - ti,spi-c2t-delay: Chip-select-active-to-transmit-start delay >> (SPIDELAY.C2TDELAY) > >> - ti,spi-t2c-delay: Transmit-end-to-chip-select-inactive delay >> (SPIDELAY.T2CDELAY) > > Now I look at these they look very much like the standard delay feature > that the SPI subsystem has already - are they? Mark, As Grygorii explained in previous postings (reproduced below), these delays are handled by the SPI hardware on Keystone and affect the delay between successive word tranmssion and has nothing to do with the delay you are talking about. Isn't the standard delay you mention here is between successive packets send down to the lower level driver (in this case spi-davinci.c) ? Murali Below is timing diagram which shows, in general, how these new parameters affect on words transmission over Keystone/Davinci SPI bus: +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ SPI_CLK | | | | | | | | | | | | | | | | +----------+ +-+ +-+ +-+ +-+ +---------------------------+ +-+ +-+ +- SPI_SOMI/SIMO+-----------------+ +----------- +----------+ word1 +---------------------------+word2 +-----------------+ +----------- WDELAY <---------> + + SPI_CS | | +----+ +-----------+ | | | +-----+-----------------+--------+ +-----+------------ | | | | | | + + + | + + <---> <------> <---> C2TDELAY T2CDELAY C2TDELAY Where: WDELAY - Delay in between transmissions C2TDELAY - Chip-select-active-to-transmit-start-delay T2CDELAY - Transmit-end-to-chip-select-inactive-delay