From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 2/3] dma: add __must_check annotation for dmaengine_pause() Date: Tue, 11 Aug 2015 14:34:29 +0200 Message-ID: <55C9EBD5.3090203@linutronix.de> References: <1438977619-15488-1-git-send-email-bigeasy@linutronix.de> <1438977619-15488-3-git-send-email-bigeasy@linutronix.de> <20150811095852.GW11789@localhost> <20150811100617.GD7576@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20150811100617.GD7576@n2100.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Russell King - ARM Linux , Vinod Koul Cc: peter@hurleysoftware.com, Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, nsekhar@ti.com, linux-omap@vger.kernel.org, linux-serial@vger.kernel.org, john.ogness@linutronix.de, Peter Ujfalusi List-Id: linux-omap@vger.kernel.org On 08/11/2015 12:06 PM, Russell King - ARM Linux wrote: > I think what people need to learn is that an API in the kernel which > returns an int _can_ fail - it returns an int so it _can_ return an > error code. If it _can_ return an error code, there _will_ be > implementations which _do_. > > If you don't check the return code, either your code doesn't care whether > the function was successful or not, or you're playing with fire. This is > a prime example of playing with fire. > > Let's leave the crappy userspace laziness with regard to error checking > to userspace, and keep it out of the kernel. > > Yes, the DMA engine capabilities may not be sufficient to describe every > detail of DMA engines, but that's absolutely no reason to skimp on error > checking. Had there been some kind of error checking at the site, this > problem would have been spotted before the 8250-omap driver was merged. Let me disable RX-DMA in 8250-omap code and push that stable. Then we won't need a special annotation for pause support because it remains off and is currently about one user. I browsed each driver in drivers/dma each one which does support pause supports it and all of them implement it unconditionally (ipu_idmac grabs a mutex first but this is another story). Adding error checking to 8250-omap like I have it in #1 and disabling RX-DMA in case pause fails looks be reasonable since there is nothing else that can be done I guess. Once we have the missing piece in omap-dma the RX-DMA can be enabled in 8250-omap. Does this sound like a plan we can agree on? Sebastian