Messages in this thread | | | Date | Wed, 1 Jun 2016 12:18:37 +0100 | From | Brian Starkey <> | Subject | Re: dma_declare_coherent_memory fails for RAM allocated memory |
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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 >[<c010bc30>] (unwind_backtrace) from [<c0109f70>] (show_stack+0x10/0x14) >[<c0109f70>] (show_stack) from [<c0126d80>] (__warn+0xcc/0xf8) >[<c0126d80>] (__warn) from [<c0126e40>] (warn_slowpath_fmt+0x34/0x44) >[<c0126e40>] (warn_slowpath_fmt) from [<c019c8d4>] (memremap+0x118/0x194) >[<c019c8d4>] (memremap) from [<c03b88fc>] >(dma_init_coherent_memory+0x48/0x104) >[<c03b88fc>] (dma_init_coherent_memory) from [<c03b89e4>] >(dma_declare_coherent_memory+0x2c/0x68) >[<c03b89e4>] (dma_declare_coherent_memory) from [<c0115c0c>] >(rmem_omapfb_device_init+0x34/0x64) >[<c0115c0c>] (rmem_omapfb_device_init) from [<c045b0f8>] >(of_reserved_mem_device_init+0x94/0xd8) >[<c045b0f8>] (of_reserved_mem_device_init) from [<c080aaf8>] >(omapdss_init_of+0xe4/0x154) >[<c080aaf8>] (omapdss_init_of) from [<c08033f4>] >(customize_machine+0x20/0x44) >[<c08033f4>] (customize_machine) from [<c01016b8>] >(do_one_initcall+0xac/0x158) >[<c01016b8>] (do_one_initcall) from [<c0800d64>] >(kernel_init_freeable+0xf8/0x1c8) >[<c0800d64>] (kernel_init_freeable) from [<c05519dc>] >(kernel_init+0x8/0x110) >[<c05519dc>] (kernel_init) from [<c0107258>] (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 <linux/io.h> > #include <linux/slab.h> > #include <linux/kernel.h> >+#include <linux/memblock.h> > #include <linux/module.h> > #include <linux/dma-mapping.h> > >@@ -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.
Cheers, -Brian
> >Thanks, >Ivo >
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