From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] mtd: mtk: avoid warning in mtk_ecc_encode Date: Fri, 30 Sep 2016 19:25:17 +0200 Message-ID: <201609301925.17577.arnd@arndb.de> References: <20160930163429.380785-1-arnd@arndb.de> <20160930185139.15c8be66@bbrezillon> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160930185139.15c8be66@bbrezillon> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+glpam-linux-mediatek=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Boris Brezillon Cc: Richard Weinberger , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Matthias Brugger , linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Brian Norris , David Woodhouse , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-mediatek@lists.infradead.org On Friday 30 September 2016, Boris Brezillon wrote: > > + /* copy into possibly unaligned OOB region with actual length */ > > + memcpy(data + bytes, eccdata, len); > > Is it better than > > for (i = 0; i < len; i += 4) { > u32 val = __raw_readl(ecc->regs + ECC_ENCPAR(i / 4)); > > memcpy(data + bytes + i, &val, min(len, 4)); > } > > I'm probably missing something, but what's the point of creating a > temporary buffer of 112 bytes on the stack since you'll have to copy > this data to the oob buffer at some point? I tried something like that first, but wasn't too happy with it for a number of small reasons: - __raw_readl in a driver is not usually the right API, __memcpy32_from_io uses it internally, but it's better for a driver not to rely on that, in case we need some barriers (which we may in factt need for other drivers). - the min(len,4) expression is incorrect, fixing that makes it more complicated again - I didn't like to call memcpy() multiple times, as that might get turned into an external function call (the compiler is free to optimize small memcpy calls or not). I agree that he 112 byte buffer isn't ideal either, it just seemed to be the lesser annoyance. Arnd