From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f43.google.com (mail-ee0-f43.google.com [74.125.83.43]) by kanga.kvack.org (Postfix) with ESMTP id ADA636B0031 for ; Thu, 10 Apr 2014 08:15:58 -0400 (EDT) Received: by mail-ee0-f43.google.com with SMTP id e53so2964519eek.2 for ; Thu, 10 Apr 2014 05:15:57 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v2si5754816eel.226.2014.04.10.05.15.56 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 10 Apr 2014 05:15:56 -0700 (PDT) Date: Thu, 10 Apr 2014 14:15:54 +0200 From: Jan Kara Subject: Re: [RFC] Helper to abstract vma handling in media layer Message-ID: <20140410121554.GC28404@quack.suse.cz> References: <1395085776-8626-1-git-send-email-jack@suse.cz> <53466C4A.2030107@samsung.com> <20140410103220.GB28404@quack.suse.cz> <53467B7E.5060408@xs4all.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53467B7E.5060408@xs4all.nl> Sender: owner-linux-mm@kvack.org List-ID: To: Hans Verkuil Cc: Jan Kara , Marek Szyprowski , linux-mm@kvack.org, linux-media@vger.kernel.org, "linaro-mm-sig@lists.linaro.org" , 'Tomasz Stanislawski' , Laurent Pinchart On Thu 10-04-14 13:07:42, Hans Verkuil wrote: > On 04/10/14 12:32, Jan Kara wrote: > > Hello, > > > > On Thu 10-04-14 12:02:50, Marek Szyprowski wrote: > >> On 2014-03-17 20:49, Jan Kara wrote: > >>> The following patch series is my first stab at abstracting vma handling > >> >from the various media drivers. After this patch set drivers have to know > >>> much less details about vmas, their types, and locking. My motivation for > >>> the series is that I want to change get_user_pages() locking and I want > >>> to handle subtle locking details in as few places as possible. > >>> > >>> The core of the series is the new helper get_vaddr_pfns() which is given a > >>> virtual address and it fills in PFNs into provided array. If PFNs correspond to > >>> normal pages it also grabs references to these pages. The difference from > >>> get_user_pages() is that this function can also deal with pfnmap, mixed, and io > >>> mappings which is what the media drivers need. > >>> > >>> The patches are just compile tested (since I don't have any of the hardware > >>> I'm afraid I won't be able to do any more testing anyway) so please handle > >>> with care. I'm grateful for any comments. > >> > >> Thanks for posting this series! I will check if it works with our > >> hardware soon. This is something I wanted to introduce some time ago to > >> simplify buffer handling in dma-buf, but I had no time to start working. > > Thanks for having a look in the series. > > > >> However I would like to go even further with integration of your pfn > >> vector idea. This structure looks like a best solution for a compact > >> representation of the memory buffer, which should be considered by the > >> hardware as contiguous (either contiguous in physical memory or mapped > >> contiguously into dma address space by the respective iommu). As you > >> already noticed it is widely used by graphics and video drivers. > >> > >> I would also like to add support for pfn vector directly to the > >> dma-mapping subsystem. This can be done quite easily (even with a > >> fallback for architectures which don't provide method for it). I will try > >> to prepare rfc soon. This will finally remove the need for hacks in > >> media/v4l2-core/videobuf2-dma-contig.c > > That would be a worthwhile thing to do. When I was reading the code this > > seemed like something which could be done but I delibrately avoided doing > > more unification than necessary for my purposes as I don't have any > > hardware to test and don't know all the subtleties in the code... BTW, is > > there some way to test the drivers without the physical video HW? > > You can use the vivi driver (drivers/media/platform/vivi) for this. > However, while the vivi driver can import dma buffers it cannot export > them. If you want that, then you have to use this tree: > > http://git.linuxtv.org/cgit.cgi/hverkuil/media_tree.git/log/?h=vb2-part4 Thanks for the pointer that looks good. I've also found drivers/media/platform/mem2mem_testdev.c which seems to do even more testing of the area I made changes to. So now I have to find some userspace tool which can issue proper ioctls to setup and use the buffers and I can start testing what I wrote :) Honza -- Jan Kara SUSE Labs, CR -- 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