From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756068Ab1KPQeB (ORCPT ); Wed, 16 Nov 2011 11:34:01 -0500 Received: from smtp-out-055.synserver.de ([212.40.185.55]:1184 "HELO smtp-out-054.synserver.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1755472Ab1KPQeA (ORCPT ); Wed, 16 Nov 2011 11:34:00 -0500 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 7425 Message-ID: <4EC3E619.70503@metafoo.de> Date: Wed, 16 Nov 2011 17:34:33 +0100 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20111010 Iceowl/1.0b2 Icedove/3.1.15 MIME-Version: 1.0 To: Mark Brown CC: Dimitris Papastamos , Jonathan Cameron , Michael Hennerich , linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, device-drivers-devel@blackfin.uclinux.org, drivers@analog.com Subject: Re: [PATCH 5/7] regmap: Check if a register is writable instead of readable in regcache_read References: <1321457302-8724-1-git-send-email-lars@metafoo.de> <1321457302-8724-5-git-send-email-lars@metafoo.de> <20111116161631.GK29986@opensource.wolfsonmicro.com> In-Reply-To: <20111116161631.GK29986@opensource.wolfsonmicro.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/16/2011 05:16 PM, Mark Brown wrote: > On Wed, Nov 16, 2011 at 04:28:20PM +0100, Lars-Peter Clausen wrote: > >> Currently regcache checks whether a register is readable when performing a >> cached read and returns an error if not. Change this check to test whether the >> register is writable. This makes more sense, since reading from the cache when >> the register is not readable allows the operation described above, but if the >> register is not writable there shouldn't be a value for it in the cache anyway. > > This logic doesn't entirely follow - one can have registers which are > volatile but could be read once at startup. Plus... Hm? The use case here is chips which do not support readback. So we never want to fallback to a hardware read but still want to be able to do a cached read. > >> @@ -206,7 +206,7 @@ int regcache_read(struct regmap *map, >> >> BUG_ON(!map->cache_ops); >> >> - if (!regmap_readable(map, reg)) >> + if (!regmap_writeable(map, reg)) >> return -EIO; > > ...the code winds up just looking like an obvious bug. Why? If a register is not writable we won't have anything in the cache for it. So reading from the cache for a register which is not writable doesn't make any sense.