From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754295AbbCFVsB (ORCPT ); Fri, 6 Mar 2015 16:48:01 -0500 Received: from mail-lb0-f180.google.com ([209.85.217.180]:44891 "EHLO mail-lb0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752761AbbCFVr6 (ORCPT ); Fri, 6 Mar 2015 16:47:58 -0500 From: "Grygorii.Strashko@linaro.org" X-Google-Original-From: "Grygorii.Strashko@linaro.org" Message-ID: <54FA2084.8050803@linaro.org> Date: Fri, 06 Mar 2015 23:47:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Russell King - ARM Linux CC: Andrew Morton , Arnd Bergmann , Tejun Heo , Tony Lindgren , "linux-mm@kvack.org" , linux-arm , "linux-omap@vger.kernel.org" , Laura Abbott , open list , Santosh Shilimkar , Catalin Marinas , Peter Ujfalusi Subject: Re: ARM: OMPA4+: is it expected dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64)); to fail? References: <54F8A68B.3080709@linaro.org> <20150305201753.GG29584@n2100.arm.linux.org.uk> In-Reply-To: <20150305201753.GG29584@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Russell, On 03/05/2015 10:17 PM, Russell King - ARM Linux wrote: > On Thu, Mar 05, 2015 at 08:55:07PM +0200, Grygorii.Strashko@linaro.org wrote: >> Now I can see very interesting behavior related to dma_coerce_mask_and_coherent() >> and friends which I'd like to explain and clarify. >> >> Below is set of questions I have (why - I explained below): >> - Is expected dma_coerce_mask_and_coherent(DMA_BIT_MASK(64)) and friends to fail on 32 bits HW? > > Not really. > >> - What is expected value for max_pfn: max_phys_pfn or max_phys_pfn + 1? > > mm/page_owner.c: > /* Find an allocated page */ > for (; pfn < max_pfn; pfn++) { > > drivers/base/platform.c: u32 low_totalram = ((max_pfn - 1) << PAGE_SHIFT); > drivers/base/platform.c: u32 high_totalram = ((max_pfn - 1) >> (32 - PAGE_SHIFT)); > > So, there's ample evidence that max_pfn is one more than the greatest pfn > which may be used in the system. > >> - What is expected value for struct memblock_region->size: mem_range_size or mem_range_size - 1? > > A size is a size - it's a number of bytes contained within the region. > If it is value 1, then there is exactly one byte in the region. If > there are 0x7fffffff, then there are 2G-1 bytes in the region, not 2G. Thanks - it seems clear now. >> - What is expected value to be returned by memblock_end_of_DRAM(): >> @base + @size(max_phys_addr + 1) or @base + @size - 1(max_phys_addr)? > > The last address plus one in the system. However, there's a problem here. > On a 32-bit system, phys_addr_t may be 32-bit. If it is 32-bit, then > "last address plus one" could be zero, which makes no sense. Hence, it > is artificially reduced to 0xfffff000, thereby omitting the final page. ^ this part seems not fully true now, because for ARM32 + DT the fdt.c->early_init_dt_add_memory_arch() is called instead of arm_add_memory() and it works in a different way a bit. For example, I don't see below message when reg = <0x80000000 0x80000000>: "Truncating memory at 0x80000000 to fit in 32-bit physical address space" instead memblock silently configured as memory.cnt = 0x1 memory[0x0].base = 0x80000000 memory[0x0].size = 0x7fffffff > >> Example 3 CONFIG_ARM_LPAE=y (but system really works with 32 bit address space): >> memory { >> device_type = "memory"; >> reg = <0x80000000 0x80000000>; >> }; >> >> memblock will be configured as: >> memory.cnt = 0x1 >> memory[0x0] [0x00000080000000-0x000000ffffffff], 0x80000000 bytes flags: 0x0 >> ^^^^^^^^^^ >> max_pfn = 0x00100000 >> >> The dma_coerce_mask_and_coherent() will fail in case 'Example 3' and succeed in cases 1,2. >> dma-mapping.c --> __dma_supported() >> if (sizeof(mask) != sizeof(dma_addr_t) && <== true for all OMAP4+ >> mask > (dma_addr_t)~0 && <== true for DMA_BIT_MASK(64) >> dma_to_pfn(dev, ~0) < max_pfn) { <== true only for Example 3 > > Hmm, I think this may make more sense to be "< max_pfn - 1" here, as > that would be better suited to our intention. > > The result of dma_to_pfn(dev, ~0) is the maximum PFN which we could > address via DMA, but we're comparing it with the maximum PFN in the > system plus 1 - so we need to subtract one from it. Ok. I'll try it. > > Please think about this and test this out; I'm not back to normal yet > (post-op) so I could very well not be thinking straight yet. Thanks for your comments. I hope you feel better. -- regards, -grygorii