From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754633AbbFKQh6 (ORCPT ); Thu, 11 Jun 2015 12:37:58 -0400 Received: from eusmtp01.atmel.com ([212.144.249.243]:33934 "EHLO eusmtp01.atmel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752236AbbFKQhz (ORCPT ); Thu, 11 Jun 2015 12:37:55 -0400 Message-ID: <5579B95F.9060307@atmel.com> Date: Thu, 11 Jun 2015 18:37:51 +0200 From: Cyrille Pitchen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Mark Brown CC: , , , , , , , , , Subject: Re: [PATCH v3 2/3] spi: atmel: update DT bindings documentation References: <20150609172531.GM14071@sirena.org.uk> In-Reply-To: <20150609172531.GM14071@sirena.org.uk> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.161.30.18] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 09/06/2015 19:25, Mark Brown a écrit : > 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