From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Subject: Re: [PATCH 09/14] Blackfin SPI driver: Fix SPI driver to work with SPI flash ST25P16 on bf548 Date: Wed, 31 Oct 2007 00:11:33 -0700 Message-ID: <200710310011.33545.david-b@pacbell.net> References: <1193735885-8202-1-git-send-email-bryan.wu@analog.com> <200710301305.02640.david-b@pacbell.net> <1193813431.6971.24.camel@roc-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Sonic Zhang , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: bryan.wu-OyLXuOCK7orQT0dZR+AlfA@public.gmane.org Return-path: In-Reply-To: <1193813431.6971.24.camel@roc-laptop> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-spi.vger.kernel.org On Tuesday 30 October 2007, Bryan Wu wrote: > Maybe there are some confusion of mixing up the spi_trasnfer.speed_hz > with the spi_device.max_speed_hz. > > spi_device.max_speed_hz comes from spi_board_info.max_speed_hz, it is > for the default max speed value. It's initialized from board_info, yes. Drivers can override it using spi_setup(). One would expect they only override _downwards_ but that's not guaranteed anywhere. A driver might have a way to establish that this particular board can run faster, for example. > spi_transfer.speed_hz comes from upper applications for each spi > transfer setting. Certainly; all spi_transfer records come from applications! If that value is zero, that transfer segment uses the limit from the spi_device ... otherwise, it can differ. Again, the limits can vary based on devise characteristics; maybe it can't feed data as fast for some commands. (ISTR the M25P16 in $SUBJECT has two read commands, one of which is only usable at clock rates below 33 MHz or so, but most other commands can work above that speed just fine.) - Dave ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/