From: cyrille.pitchen@atmel.com (Cyrille Pitchen) Date: Thu, 11 Jun 2015 18:37:51 +0200 Subject: [PATCH v3 2/3] spi: atmel: update DT bindings documentation In-Reply-To: <20150609172531.GM14071@sirena.org.uk> References: <20150609172531.GM14071@sirena.org.uk> Message-ID: <5579B95F.9060307@atmel.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Le 09/06/2015 19:25, Mark Brown a ?crit : > On Tue, Jun 09, 2015 at 01:53:53PM +0200, Cyrille Pitchen wrote: >> - add new property "atmel,fifo-size" > > Why is this a property and not something we know from the IP version? > Hi Mark, Please be aware that the VERSION register can not be used to guess the size of FIFOs. Indeed, for a given hardware version, the SPI controller can be integrated on Atmel SoCs with different FIFO sizes. Also the "atmel,fifo-size" property is optional as older SPI controllers don't embed FIFO at all. Besides, the FIFO size can not be read or guessed from other registers: When designing the FIFO feature, no dedicated registers were added to store this size. Unused spaces in the I/O register range are limited and better reserved for future usages. Instead, the FIFO size of each peripheral is documented in the programmer datasheet. Finally, on a given SoC, there can be several instances of the SPI controller with different FIFO sizes. This explain why we'd rather use a dedicated DT property than use the "compatible" property. I hope these pieces of information will help to clarify this point. Of course, we are open to other suggestions. Best Regards, Cyrille