From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932343AbcHSCEp (ORCPT ); Thu, 18 Aug 2016 22:04:45 -0400 Received: from aserp1050.oracle.com ([141.146.126.70]:29390 "EHLO aserp1050.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755150AbcHSCEK (ORCPT ); Thu, 18 Aug 2016 22:04:10 -0400 Subject: Re: [PATCH 1/1] ARM: dma: fix dma_max_pfn() To: Russell King - ARM Linux References: <1471435517-7840-1-git-send-email-rogerq@ti.com> <1471435517-7840-2-git-send-email-rogerq@ti.com> <20160818142459.GX1041@n2100.armlinux.org.uk> <8003b6ed-6071-9384-1b88-0b84604bdce8@oracle.com> <20160818230754.GE1041@n2100.armlinux.org.uk> Cc: Roger Quadros , ssantosh@kernel.org, grygorii.strashko@ti.com, linux-arm-kernel@lists.infradead.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Greg Kroah-Hartman , Arnd Bergmann , Olof Johansson , Catalin Marinas , Linus Walleij From: Santosh Shilimkar Organization: Oracle Corporation Message-ID: Date: Thu, 18 Aug 2016 19:01:47 -0700 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160818230754.GE1041@n2100.armlinux.org.uk> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserp1040.oracle.com [141.146.126.69] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/18/2016 4:07 PM, Russell King - ARM Linux wrote: > On Thu, Aug 18, 2016 at 09:55:55AM -0700, Santosh Shilimkar wrote: >> Hi Russell, >> >> On 8/18/2016 7:24 AM, Russell King - ARM Linux wrote: >>> On Wed, Aug 17, 2016 at 03:05:17PM +0300, Roger Quadros wrote: >>>> Since commit 6ce0d2001692 ("ARM: dma: Use dma_pfn_offset for dma address translation"), >>>> dma_to_pfn() already returns the PFN with the physical memory start offset >>>> so we don't need to add it again. >>>> >>>> This fixes USB mass storage lock-up problem on systems that can't do DMA >>>> over the entire physical memory range (e.g.) Keystone 2 systems with 4GB RAM >>>> can only do DMA over the first 2GB. [K2E-EVM]. >>>> >>>> What happens there is that without this patch SCSI layer sets a wrong >>>> bounce buffer limit in scsi_calculate_bounce_limit() for the USB mass >>>> storage device. dma_max_pfn() evaluates to 0x8fffff and bounce_limit >>>> is set to 0x8fffff000 whereas maximum DMA'ble physical memory on Keystone 2 >>>> is 0x87fffffff. This results in non DMA'ble pages being given to the >>>> USB controller and hence the lock-up. >>>> >>>> NOTE: in the above case, USB-SCSI-device's dma_pfn_offset was showing as 0. >>>> This should have really been 0x780000 as on K2e, LOWMEM_START is 0x80000000 >>>> and HIGHMEM_START is 0x800000000. DMA zone is 2GB so dma_max_pfn should be >>>> 0x87ffff. The incorrect dma_pfn_offset for the USB storage device is because >>>> USB devices are not correctly inheriting the dma_pfn_offset from the >>>> USB host controller. This will be fixed by a separate patch. >>> >>> I'd like to hear from Santosh, as the author of the original change. >>> The original commit doesn't mention which platform it was intended for >>> or what the problem was, which would've been helpful. >>> >> From what I recollect, we did these changes to make the max pfn behave >> same on ARM arch as other archs. This patch was evolved as part of >> fixing the max*pfn assumption. > > To me, the proposed patch _looks_ correct, because... > >>>> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h >>>> index d009f79..bf02dbd 100644 >>>> --- a/arch/arm/include/asm/dma-mapping.h >>>> +++ b/arch/arm/include/asm/dma-mapping.h >>>> @@ -111,7 +111,7 @@ static inline dma_addr_t virt_to_dma(struct device *dev, void *addr) >>>> /* The ARM override for dma_max_pfn() */ >>>> static inline unsigned long dma_max_pfn(struct device *dev) >>>> { >>>> - return PHYS_PFN_OFFSET + dma_to_pfn(dev, *dev->dma_mask); >>>> + return dma_to_pfn(dev, *dev->dma_mask); >>>> } >>>> #define dma_max_pfn(dev) dma_max_pfn(dev) >> By doing this change I hope we don't break other drivers on Keystone so >> am not sure about the change. > > dma_to_pfn() returns the page frame number referenced from physical > address zero - the default implementation of dma_to_pfn() is > bus_to_pfn(), which is __phys_to_pfn(x), which is just x >> PAGE_SHIFT. > The other thing about dma_to_pfn() is that it should return a > zero-referenced PFN number, where PFN 0 = physical address 0. > > If there is some offset for keystone2, that should be taken care of > via "dev->dma_pfn_offset", and not offsetting the return value from > dma_to_pfn(). > > So I'm 99.9% convinced that the proposed change is correct. > I will got with that then :-) and take my objection back. Just saying that if there other breakages which I can't recollect now, those drivers needs to be patched as well.