From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v5] spi: orion.c: Add direct access mode Date: Mon, 18 Apr 2016 13:32:49 +0200 Message-ID: <4248364.c0REkIZjj0@wuerfel> References: <1460974417-32375-1-git-send-email-sr@denx.de> <4437692.8jaX7AeWuo@wuerfel> <20160418110415.GT3217@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: Stefan Roese , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Thomas Petazzoni , Gregory CLEMENT , Andrew Lunn To: Mark Brown Return-path: In-Reply-To: <20160418110415.GT3217-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: On Monday 18 April 2016 12:04:15 Mark Brown wrote: > On Mon, Apr 18, 2016 at 12:51:55PM +0200, Arnd Bergmann wrote: > > > This would be easier if have a conclusive proof that 1MB per CS always enough. > > Is this something that is guaranteed in the SPI spec or the documentation for > > this controller? > > There's no spec for SPI but if there were it'd be hard to see it > imposing a limit, one can transfer data as long as the bus is clocked > (which some things like ADCs and DACs make use of). > I just reread Stefan's patch and realized that I had fundamentally misunderstood how the transfer is done: I thought the offset inside of the window was used to address a NOR flash directly, but it seems it is just used to send arbitrarily long commands. This means that the 1MB window is probably a reasonable size (provided that the (most importantly) the SPI-NOR driver can guarantee that it never exceeds this). It also means that we are probably better off using the single-window mode of the SPI controller, where all CS lines share a single mbus window. The only real difference here is that we can map all endpoints using a single contiguous window into the CPU address space if we want, or we can still map them separately on a given board if that results in a nicer layout. Arnd -- 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