Date: Wed, 27 May 2009 13:55:26 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Piotr =?utf-8?q?Zi=C4=99cik?= <kosmo@semihalf.com> Subject: Re: Generic ATA driver DMA coherency issues Message-ID: <200905271355.28791.jhb@freebsd.org> In-Reply-To: <200905271253.06693.kosmo@semihalf.com> References: <200905271253.06693.kosmo@semihalf.com>
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On Wednesday 27 May 2009 6:53:06 am Piotr Zi=C4=99cik wrote: > While working on bring-up SATA on ARM SoC I had issues with DMA memory=20 > coherency. After tracing, I have found problem in generic ATA code=20 behaviour. >=20 > The ATA generic driver allocates 64k DMA workspace memory which can be=20 > optionally used by ATA chipset drivers. Currently only ata-ahci,=20 ata-marvell,=20 > ata-promise and ata-siliconimage relies on this feature. In general, the= =20 > drivers use preallocated DMA workspace to hold small request descriptors,= =20 > consumed by hardware. >=20 > All of these drivers do not synchronize workspace with bus_dmamap_sync().= =20 They=20 > assumes that DMA workspace is coherent. However ATA driver neither enforc= es=20 > coherency by using BUS_DMA_COHERENT flag nor synchronizes the workspace w= ith=20 > bus_dmamap_sync(). >=20 > I have fixed my problem by adding BUS_DMA_COHERENT flag to workspace=20 > allocation code: >=20 > diff --git a/sys/dev/ata/ata-dma.c b/sys/dev/ata/ata-dma.c > index ab4c3c8..71ee41b 100644 > --- a/sys/dev/ata/ata-dma.c > +++ b/sys/dev/ata/ata-dma.c > @@ -95,8 +95,8 @@ ata_dmainit(device_t dev) > 0, NULL, NULL, &ch->dma.work_tag)) > goto error; >=20 > - if (bus_dmamem_alloc(ch->dma.work_tag, (void **)&ch->dma.work, 0, > - &ch->dma.work_map)) > + if (bus_dmamem_alloc(ch->dma.work_tag, (void **)&ch->dma.work, > + BUS_DMA_COHERENT, &ch->dma.work_map)) > goto error; >=20 > if (bus_dmamap_load(ch->dma.work_tag, ch->dma.work_map, ch->dma.work, >=20 > The question is about multiplatform impact of this change. Especially I a= m=20 > curious how everything works without any problems on i386. The flag has no effect on x86. =2D-=20 John Baldwin
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