Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752714AbaKJLxd (ORCPT ); Mon, 10 Nov 2014 06:53:33 -0500 Received: from mail-ig0-f174.google.com ([209.85.213.174]:60032 "EHLO mail-ig0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbaKJLxb convert rfc822-to-8bit (ORCPT ); Mon, 10 Nov 2014 06:53:31 -0500 MIME-Version: 1.0 In-Reply-To: References: <1413871011-4101-1-git-send-email-ankit.jindal@linaro.org> <1413871011-4101-3-git-send-email-ankit.jindal@linaro.org> <6D33D50E-2DD1-482C-B05E-45B237F3B779@codeaurora.org> <4B098F57-E202-412C-B54D-085A46792EDC@codeaurora.org> From: Ankit Jindal Date: Mon, 10 Nov 2014 17:23:10 +0530 Message-ID: Subject: Re: [PATCH v3 2/6] uio: Add new UIO_MEM_PHYS_CACHE type for mem regions To: Kumar Gala Cc: "linux-kernel@vger.kernel.org" , "Hans J. Koch" , Greg Kroah-Hartman , "patches@apm.com" , "linux-arm-kernel@lists.infradead.org" , Rob Herring , Tushar Jagad , Russell King - ARM Linux , "devicetree@vger.kernel.org" , Guenter Roeck , Varka Bhadram Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5 November 2014 20:39, Kumar Gala wrote: > > On Nov 5, 2014, at 6:55 AM, Ankit Jindal wrote: > >> Hi Kumar, >> >> On 31 October 2014 19:09, Kumar Gala wrote: >>> >>> On Oct 31, 2014, at 4:30 AM, Ankit Jindal wrote: >>> >>>> Hi Kumar, >>>> >>>> On 21 October 2014 12:08, Kumar Gala wrote: >>>>> >>>>> On Oct 21, 2014, at 7:56 AM, Ankit Jindal wrote: >>>>> >>>>>> Currently, three types of mem regions are supported: UIO_MEM_PHYS, >>>>>> UIO_MEM_LOGICAL and UIO_MEM_VIRTUAL. Among these UIO_MEM_PHYS helps >>>>>> UIO driver export physcial memory to user space as non-cacheable >>>>>> user memory. Typcially memory-mapped registers of a device are exported >>>>>> to user space as UIO_MEM_PHYS type mem region. The UIO_MEM_PHYS type >>>>>> is not efficient if dma-capable devices are capable of maintaining coherency >>>>>> with CPU caches. >>>>>> >>>>>> This patch adds new type UIO_MEM_PHYS_CACHE for mem regions to enable >>>>>> cacheable access to physical memory from user space. >>>>>> >>>>>> Signed-off-by: Ankit Jindal >>>>>> Signed-off-by: Tushar Jagad >>>>>> --- >>>>>> drivers/uio/uio.c | 11 ++++++++--- >>>>>> include/linux/uio_driver.h | 1 + >>>>>> 2 files changed, 9 insertions(+), 3 deletions(-) >>>>> >>>>> Rather than adding a new type, why not allow the driver to set the pgprot value, this way one has full control and we don’t need to keep adding types for various different cache attributions in the future. >>>> >>>> Do you mean to add a new field pgprot_t in the memtype structure and >>>> uio_mmap_physical will set vma->vm_page_prot to this value provided by >>>> driver ? If this is the case then we will need to change all the >>>> current uio based drivers which was the reason I preferred to have a >>>> new mem type. >>>> >>>> Please let me know if I have misunderstood anything. >>> >>> I’m suggeting in uio_mmap_physical to do something like: >>> >>> if (idev->info->set_pgprot) >>> idev->info->set_pgprot(vma->vm_page_prot) >>> else >>> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); >>> >>> And add a set_prprot callback to 'struct uio_info’. >>> >>> Here’s patch from several years ago: >>> >>> http://patchwork.ozlabs.org/patch/119224/ >> >> The suggested solution looks okey but not sure whether there is any >> available drivers using different combinations. Also, I looked at the >> available pgprot routines, looks like only pgprot_noncached and >> pgprot_writecombine are the available ones. So if we are not going to >> use these pgprot routines then driver might have architecture >> dependent switches, which we should avoid. > > There are cases that are arch/driver specific that do not fall into pgprot_noncached or pgprot_writecombine. So I don’t see why we should limit them. For example the Freescale networking guys need cacheable-noncoherent for some of their UIO work. > > We can deal with arch specific issues during review of the UIO driver themselves. Ok. But, in our case we do not want to set any special attribute, instead just want to avoid setting non-cacheable attribute. So if we go by the approach as in your patch, then I need to register a dummy routine which does nothing. I think another approach could be to have new mem type as in this patch and add something like this to this patch: if (cacheable) { /* check if driver want to set any special cacheable attribute combination */ if (idev->info->set_pgprot) idev->info->set_pgprot(vma->vm_page_prot) } else { vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); } Please let me know your view. > - k > > -- > Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project > Thanks, Ankit -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/