Messages in this thread | | | Date | Tue, 27 Sep 2011 15:49:23 +0300 | From | Felipe Balbi <> | Subject | Re: [PATCH] x86/dma: make a zero length mapping length not dma capable |
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hi,
On Tue, Sep 20, 2011 at 07:44:25PM +0200, Sebastian Andrzej Siewior wrote: > The following ooops happens during a call to dma_map_single(): > > | ------------[ cut here ]------------ > | kernel BUG at lib/swiotlb.c:409! > | invalid opcode: 0000 [#1] SMP > | CPU 1 > | > | RIP: 0010:[<ffffffff811a00c9>] [<ffffffff811a00c9>] swiotlb_tbl_map_single+0x87/0x1e0 > | Call Trace: > | [<ffffffff813170e0>] ? printk+0x43/0x48 > | [<ffffffff8100d027>] ? load_TLS+0x7/0xa > | [<ffffffff811a0261>] ? map_single+0x3f/0x3f > | [<ffffffff811a02be>] ? swiotlb_map_page+0x5d/0xcd > | [<ffffffff811a0261>] ? map_single+0x3f/0x3f > | [<ffffffffa02946ca>] ? dwc3_map_buffer_to_dma+0x8a/0xe2 [dwc3] > > As you know from the line 409 the size parameter was 0. This happens > because the upper layer sends a zero length packet which the dwc3 driver > tried to map. > The memory is not really used and the hardware should not really issue a > dma request however we must setup a dma descriptor which contains an > address field and a size field which is set to 0 for the zero length > packet to be sent. So the unconditional mapping was kinda convenient to > do. ARM does not complain about length == 0, the swiotlb which is > used on x86 makes trouble. Looking at other udc drivers, they either > ignore this case or workaround it by incrementing the size by 1 which > looks nasty. > For now I fixed this by not mapping zero packets at all. Anything what I > should expect from the DMA API? I.e. should it be okay to call > dma_map_single() with size = 0? > This patch is untested due to -ENODEV. Changing each implementation of > dma_map_single() will result in large patch and it is also question if > this is worth the effort. > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This helps my dwc3 driver:
Acked-by: Felipe Balbi <balbi@ti.com>
> --- > arch/x86/include/asm/dma-mapping.h | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h > index d4c419f..e73d921 100644 > --- a/arch/x86/include/asm/dma-mapping.h > +++ b/arch/x86/include/asm/dma-mapping.h > @@ -65,6 +65,8 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size) > { > if (!dev->dma_mask) > return 0; > + if (!size) > + return 0; > > return addr + size - 1 <= *dev->dma_mask; > } > -- > 1.7.6.3 >
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