From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by wa-out-1112.google.com with SMTP id j37so115376waf.22 for ; Fri, 05 Dec 2008 16:32:31 -0800 (PST) Message-ID: <208aa0f00812051632h38fc0a5g58d233190436cc90@mail.gmail.com> Date: Fri, 5 Dec 2008 16:32:30 -0800 From: "Edward Estabrook" Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA In-Reply-To: <20081205094447.GA3081@local> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <43FC624C55D8C746A914570B66D642610367F29B@cos-us-mb03.cos.agilent.com> <1228379942.5092.14.camel@twins> <20081204180809.GB3079@local> <1228461060.18899.8.camel@twins> <20081205094447.GA3081@local> Sender: owner-linux-mm@kvack.org Return-Path: To: "Hans J. Koch" Cc: Peter Zijlstra , edward_estabrook@agilent.com, linux-kernel@vger.kernel.org, gregkh@suse.de, edward.estabrook@gmail.com, hugh , linux-mm , Thomas Gleixner List-ID: > Well, UIO already rapes the mmap interface by using the "offset" parameter to > pass in the number of the mapping. Exactly. > But I'll NAK the current concept, too. It's a UIO kernel driver's task to tell > userspace which memory a device has to offer. The UIO core prevents userspace > as much as possible from mapping anything different. And it should stay that > way. The ultimate purpose (I thought) of the UIO driver is to simplify driver development by pushing device control into userspace. There is a very real need for efficient dynamic control over the DMA allocation of a device. Why not 'allow' this to happen in userspace if it can be done safely and without breaking anything else? Remember that for devices employing ring buffers it is not a question of 'how much memory a device has to offer' but rather 'how much system memory would the driver like to configure that device to use'. I don't want to stop my DMA engine and reload the driver to create more buffers (and I don't want to pre-allocate more than I need as contingency). Cheers, Ed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org