From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ivaylo Dimitrov Subject: Re: dma_declare_coherent_memory fails for RAM allocated memory Date: Sat, 4 Jun 2016 23:14:44 +0300 Message-ID: <575336B4.4080508@gmail.com> References: <574B0302.3010809@gmail.com> <20160601111837.GA10691@e106950-lin.cambridge.arm.com> <5750696B.4070108@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5750696B.4070108@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Brian Starkey Cc: LKML , Greg Kroah-Hartman , "linux-omap@vger.kernel.org" , sebastian Reichel , =?UTF-8?Q?Pali_Roh=c3=a1r?= , Tony Lindgren List-Id: linux-omap@vger.kernel.org On 2.06.2016 20:14, Ivaylo Dimitrov wrote: > Hi, > > On 1.06.2016 14:18, Brian Starkey wrote: >> Hi Ivo, >> >> On Sun, May 29, 2016 at 05:56:02PM +0300, Ivaylo Dimitrov wrote: >>> Hi, >>> >>> When trying to declare and use DT reserved memory region on ARM >>> (OMAP3), dma_declare_coherent_memory() fails in memremap(). This is >>> from today's master: >>> >>> ------------[ cut here ]------------ >>> WARNING: CPU: 0 PID: 1 at kernel/memremap.c:111 memremap+0x118/0x194 >>> memremap attempted on ram 0x8f800000 size: 0x700000 >>> Modules linked in: >>> CPU: 0 PID: 1 Comm: swapper Not tainted 4.6.0+ #15 >>> Hardware name: Nokia RX-51 board >>> [] (unwind_backtrace) from [] (show_stack+0x10/0x14) >>> [] (show_stack) from [] (__warn+0xcc/0xf8) >>> [] (__warn) from [] (warn_slowpath_fmt+0x34/0x44) >>> [] (warn_slowpath_fmt) from [] >>> (memremap+0x118/0x194) >>> [] (memremap) from [] >>> (dma_init_coherent_memory+0x48/0x104) >>> [] (dma_init_coherent_memory) from [] >>> (dma_declare_coherent_memory+0x2c/0x68) >>> [] (dma_declare_coherent_memory) from [] >>> (rmem_omapfb_device_init+0x34/0x64) >>> [] (rmem_omapfb_device_init) from [] >>> (of_reserved_mem_device_init+0x94/0xd8) >>> [] (of_reserved_mem_device_init) from [] >>> (omapdss_init_of+0xe4/0x154) >>> [] (omapdss_init_of) from [] >>> (customize_machine+0x20/0x44) >>> [] (customize_machine) from [] >>> (do_one_initcall+0xac/0x158) >>> [] (do_one_initcall) from [] >>> (kernel_init_freeable+0xf8/0x1c8) >>> [] (kernel_init_freeable) from [] >>> (kernel_init+0x8/0x110) >>> [] (kernel_init) from [] (ret_from_fork+0x14/0x3c) >>> ---[ end trace 73a8c076df72166b ]--- >>> omapfb: dma_declare_coherent_memory failed >>> >>> >>> The failing code looks like: >>> . >>> . >>> . >>> static int rmem_omapfb_device_init(struct reserved_mem *rmem, struct >>> device *dev) >>> { >>> int dma; >>> >>> if (rmem->priv) >>> return 0; >>> >>> dma = dma_declare_coherent_memory(&omap_fb_device.dev, rmem->base, >>> rmem->base, rmem->size, >>> DMA_MEMORY_MAP | >>> DMA_MEMORY_EXCLUSIVE); >>> if (!(dma & DMA_MEMORY_MAP)) { >>> pr_err("omapfb: dma_declare_coherent_memory failed\n"); >>> return -ENOMEM; >>> } >>> else >>> rmem->priv = omap_fb_device.dev.dma_mem; >>> >>> return 0; >>> } >>> >>> static void rmem_omapfb_device_release(struct reserved_mem *rmem, >>> struct device *dev) >>> { >>> dma_release_declared_memory(&omap_fb_device.dev); >>> } >>> >>> static const struct reserved_mem_ops rmem_omapfb_ops = { >>> .device_init = rmem_omapfb_device_init, >>> .device_release = rmem_omapfb_device_release, >>> }; >>> >>> static int __init rmem_omapfb_setup(struct reserved_mem *rmem) >>> { >>> rmem->ops = &rmem_omapfb_ops; >>> pr_info("omapfb: reserved %d bytes at %pa\n", rmem->size, >>> &rmem->base); >>> >>> return 0; >>> } >>> >>> RESERVEDMEM_OF_DECLARE(dss, "ti,omapfb-memsize", rmem_omapfb_setup); >>> >>> >>> It turns out that dma_init_coherent_memory calls memremap with >>> MEMREMAP_WC flag, which is disallowed for RAM IIUC. >>> >> >> Right. If you want to use a memory region as coherent DMA memory, then >> that same region can't be System RAM, because System RAM is usually >> mapped in a non-coherent fashion. >> >>> I quickly hacked some code to fix the issue, but as memremap API is >>> relatively new(esp to me), I wonder if this is the correct way to go: >>> >>> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c >>> index bdf28f7..04b1687 100644 >>> --- a/drivers/base/dma-coherent.c >>> +++ b/drivers/base/dma-coherent.c >>> @@ -5,6 +5,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> >>> @@ -32,8 +33,12 @@ static bool dma_init_coherent_memory( >>> if (!size) >>> goto out; >>> >>> - if (flags & DMA_MEMORY_MAP) >>> - mem_base = memremap(phys_addr, size, MEMREMAP_WC); >>> + if (flags & DMA_MEMORY_MAP) { >>> + unsigned long map_type = >>> memblock_is_map_memory(phys_addr) ? >>> + MEMREMAP_WB : >>> MEMREMAP_WC; >>> + >>> + mem_base = memremap(phys_addr, size, map_type); >>> + } >>> else >>> mem_base = ioremap(phys_addr, size); >>> if (!mem_base) >>> >>> Does the above code looks sane? How to fix the problem if not? >> >> AFAIK dma_declare_coherent_memory() should only be used on physical >> addresses which don't already have a CPU virtual mapping. Certainly >> returning (potentially) cached memory as DMA coherent is asking for >> trouble. >> >> I think what you want to do is add a "no-map;" property to your >> reserved-memory region in DT. That will stop the kernel from using it >> as System RAM, leaving it free for your framebuffer. >> > > I tried to use "no-map", but for some reason it doesn't allow me to > allocate more than 2MB, anything above results in: > > qemu: fatal: Trying to execute code outside RAM or ROM at 0xffff0010 > > R00=22222220 R01=cf901000 R02=cfaffff4 R03=e0000000 > R04=0008ff80 R05=00090000 R06=00000000 R07=c096333c > R08=c0904dc0 R09=c093a23c R10=00000001 R11=c0727b3b > R12=0000ff80 R13=c093af8c R14=c082aba0 R15=ffff0010 > PSR=a00001d7 N-C- A abt32 > Aborted (core dumped) > > I was able to track the code to memblock_isolate_range() - if I return > -ENOMEM on http://lxr.free-electrons.com/source/mm/memblock.c#L671, the > above crash does not occur(however the allocation fails as well). > Putting some printks doesn't reveal anything suspicious to me: > > for 2MB: > > [ 0.000000] base 8fe00000, size 200000, rgn->base 80000000, rgn->size > 10000000, type->total_size 10000000 > [ 0.000000] base - rbase fe00000 > > > for 4MB: > > [ 0.000000] base 8fc00000, size 400000, rgn->base 80000000, rgn->size > 10000000, type->total_size 10000000 > [ 0.000000] base - rbase fc00000 > > > However, this is where my limited memblock knowledge ends, so any help > is appreciated. > It turned out I have to increase CONFIG_FORCE_MAX_ZONEORDER in order to be able to use more than 2MB of allocated memory. Ivo