30 Jul 22:24 2012
About dma_sync_single_for_{cpu,device}
Hi, On our board we've got an MV78200 and a network device between which we xfer memory chunks via the ddram with an external dma controller. To handle these xfers we're using the dma API. To tx a chunk of data from the SoC => network device, we : - prepare a buffer with a leading header embedding a pattern, - trigger the xfer and wait for an irq // The device updates the pattern and then triggers an irq - upon irq we check the pattern for the xfer completion I was expecting the following to work: addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); dev_send(buffer); // wait for irq (don't peek in the buffer) ... got irq dma_sync_single_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); if (!xfer_done(buffer)) // not RAM value dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); [...] But this does not work (the buffer pattern does not reflect the ddram value). On the other hand, the following works: [...] // wait for irq (don't peek in the buffer) ... got irq dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); if (!xfer_done(buffer)) // RAM value [...](Continue reading)
30 Jul 22:34 2012
Re: About dma_sync_single_for_{cpu,device}
On Mon, Jul 30, 2012 at 10:24:01PM +0200, karl.beldan <at> gmail.com wrote: > I was expecting the following to work: > addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); Sorry, I forgot this (invalidate): dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > dev_send(buffer); > // wait for irq (don't peek in the buffer) ... got irq > dma_sync_single_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); > if (!xfer_done(buffer)) // not RAM value > dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > [...] Karl
31 Jul 08:45 2012
Re: About dma_sync_single_for_{cpu,device}
Hi, (This is an email originally addressed to the linux-kernel mailing-list.) On our board we've got an MV78200 and a network device between which we xfer memory chunks via the ddram with an external dma controller. To handle these xfers we're using the dma API. To tx a chunk of data from the SoC => network device, we : - prepare a buffer with a leading header embedding a pattern, - trigger the xfer and wait for an irq // The device updates the pattern and then triggers an irq - upon irq we check the pattern for the xfer completion I was expecting the following to work: addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); dev_send(buffer); // wait for irq (don't peek in the buffer) ... got irq dma_sync_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); if (!xfer_done(buffer)) // not RAM value dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); [...] But this does not work (the buffer pattern does not reflect the ddram value). On the other hand, the following works: [...] // wait for irq (don't peek in the buffer) ... got irq(Continue reading)
31 Jul 08:59 2012
Re: About dma_sync_single_for_{cpu,device}
Karl Beldan wrote: > To tx a chunk of data from the SoC => network device, we : > - prepare a buffer with a leading header embedding a pattern, > - trigger the xfer and wait for an irq > // The device updates the pattern and then triggers an irq > - upon irq we check the pattern for the xfer completion > > I was expecting the following to work: > addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); Of both the CPU and the device write to the buffer, you must use DMA_BIDIRECTIONAL. Regards, Clemens
31 Jul 09:27 2012
Re: About dma_sync_single_for_{cpu,device}
On 7/31/12, Clemens Ladisch <clemens <at> ladisch.de> wrote: > Karl Beldan wrote: >> To tx a chunk of data from the SoC => network device, we : >> - prepare a buffer with a leading header embedding a pattern, >> - trigger the xfer and wait for an irq >> // The device updates the pattern and then triggers an irq >> - upon irq we check the pattern for the xfer completion >> >> I was expecting the following to work: >> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > > Of both the CPU and the device write to the buffer, you must use > DMA_BIDIRECTIONAL. > Hi Clemens, This does not work (tested) : seems to me BIDIRECTIONAL would just add invalidate, and invalidate before the ram has been updated, as stated, does not work. In fact the immediately following sync_for_device is intended to cater for what DMA_BIDIRECTIONAL would provide (though it is not implementation agnostic), only invalidating a smaller address range. Regards, Karl
31 Jul 09:34 2012
Re: About dma_sync_single_for_{cpu,device}
Karl Beldan wrote: > On 7/31/12, Clemens Ladisch <clemens <at> ladisch.de> wrote: >> Karl Beldan wrote: >>> To tx a chunk of data from the SoC => network device, we : >>> - prepare a buffer with a leading header embedding a pattern, >>> - trigger the xfer and wait for an irq >>> // The device updates the pattern and then triggers an irq >>> - upon irq we check the pattern for the xfer completion >>> >>> I was expecting the following to work: >>> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); >> >> Of both the CPU and the device write to the buffer, you must use >> DMA_BIDIRECTIONAL. > > This does not work (tested) : seems to me BIDIRECTIONAL would just > add invalidate, and invalidate before the ram has been updated, as > stated, does not work. Please show the exact sequence of dma_* calls, and also show when and how the CPU and the device access the buffer. Regards, Clemens
31 Jul 10:30 2012
Re: About dma_sync_single_for_{cpu,device}
On Tue, Jul 31, 2012 at 09:34:01AM +0200, Clemens Ladisch wrote: > Karl Beldan wrote: > > On 7/31/12, Clemens Ladisch <clemens <at> ladisch.de> wrote: > >> Karl Beldan wrote: > >>> To tx a chunk of data from the SoC => network device, we : > >>> - prepare a buffer with a leading header embedding a pattern, > >>> - trigger the xfer and wait for an irq > >>> // The device updates the pattern and then triggers an irq > >>> - upon irq we check the pattern for the xfer completion > >>> > >>> I was expecting the following to work: > >>> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > >> > >> Of both the CPU and the device write to the buffer, you must use > >> DMA_BIDIRECTIONAL. > > > > This does not work (tested) : seems to me BIDIRECTIONAL would just > > add invalidate, and invalidate before the ram has been updated, as > > stated, does not work. > > Please show the exact sequence of dma_* calls, and also show when and > how the CPU and the device access the buffer. > Hmm, so I just spotted a line where we peek in the buffer after invalidating .. cannot believe I missed it .. so sorry for the noise .. now it's working. I felt I would find the culprit right after posting ;) Thanks Clemens !
31 Jul 11:09 2012
Re: About dma_sync_single_for_{cpu,device}
On Tue, Jul 31, 2012 at 08:45:57AM +0200, Karl Beldan wrote: > I was expecting the following to work: > addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > dev_send(buffer); > // wait for irq (don't peek in the buffer) ... got irq > dma_sync_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); > if (!xfer_done(buffer)) // not RAM value > dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > [...] First point is that you clearly do not understand the DMA API at all. The DMA API has the idea of buffer ownership. Only the owner may access the buffer: *CPU OWNS THE BUFFER* dma_map_single() *DEVICE OWNS THE BUFFER* dma_sync_single_for_cpu() *CPU OWNS THE BUFFER* dma_sync_single_for_device() *DEVICE OWNS THE BUFFER* dma_unmap_single() *CPU OWNS THE BUFFER* So, there is absolutely no noeed what so ever to follow dma_map_single() with dma_sync_single_for_device(). Second point is that you should not change the 'direction' argument while a buffer is mapped.(Continue reading)
31 Jul 21:31 2012
Re: About dma_sync_single_for_{cpu,device}
On 7/31/12, Russell King - ARM Linux <linux <at> arm.linux.org.uk> wrote: > On Tue, Jul 31, 2012 at 08:45:57AM +0200, Karl Beldan wrote: >> I was expecting the following to work: >> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); >> dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); >> dev_send(buffer); >> // wait for irq (don't peek in the buffer) ... got irq >> dma_sync_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); >> if (!xfer_done(buffer)) // not RAM value >> dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); >> [...] > Hi Russell, > First point is that you clearly do not understand the DMA API at all. The > DMA API has the idea of buffer ownership. Only the owner may access the > buffer: > Are you saying that this scenario does not work ? We are taking some liberties with the DMA API, we're more using some of its funcs rather than _using_ it ;). The question was not whether this was a proper usage of the API, but why that scenario would not lead to the expected results .. and now I've found the culprit peek I am happy. [...] > So, there is absolutely no noeed what so ever to follow dma_map_single() > with dma_sync_single_for_device(). >(Continue reading)
31 Jul 22:08 2012
Re: About dma_sync_single_for_{cpu,device}
On Tue, Jul 31, 2012 at 09:31:13PM +0200, Karl Beldan wrote: > On 7/31/12, Russell King - ARM Linux <linux <at> arm.linux.org.uk> wrote: > > On Tue, Jul 31, 2012 at 08:45:57AM +0200, Karl Beldan wrote: > >> I was expecting the following to work: > >> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > >> dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > >> dev_send(buffer); > >> // wait for irq (don't peek in the buffer) ... got irq > >> dma_sync_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); > >> if (!xfer_done(buffer)) // not RAM value > >> dma_sync_single_for_device(dev, buffer, pattern_size, DMA_FROM_DEVICE); > >> [...] > > > > Hi Russell, > > > > First point is that you clearly do not understand the DMA API at all. The > > DMA API has the idea of buffer ownership. Only the owner may access the > > buffer: > > > Are you saying that this scenario does not work ? > We are taking some liberties with the DMA API, we're more using some > of its funcs rather than _using_ it ;). > The question was not whether this was a proper usage of the API, but > why that scenario would not lead to the expected results .. and now > I've found the culprit peek I am happy. If you abuse the API don't expect your stuff to work in future kernel versions.(Continue reading)
1 Aug 08:50 2012
Re: About dma_sync_single_for_{cpu,device}
On 7/31/12, Russell King - ARM Linux <linux <at> arm.linux.org.uk> wrote: > On Tue, Jul 31, 2012 at 09:31:13PM +0200, Karl Beldan wrote: >> On 7/31/12, Russell King - ARM Linux <linux <at> arm.linux.org.uk> wrote: >> > On Tue, Jul 31, 2012 at 08:45:57AM +0200, Karl Beldan wrote: >> >> I was expecting the following to work: >> >> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); >> >> dma_sync_single_for_device(dev, buffer, pattern_size, >> >> DMA_FROM_DEVICE); >> >> dev_send(buffer); >> >> // wait for irq (don't peek in the buffer) ... got irq >> >> dma_sync_single_for_cpu(dev, buffer, pattern_size, DMA_FROM_DEVICE); >> >> if (!xfer_done(buffer)) // not RAM value >> >> dma_sync_single_for_device(dev, buffer, pattern_size, >> >> DMA_FROM_DEVICE); >> >> [...] >> > >> >> Hi Russell, >> >> >> > First point is that you clearly do not understand the DMA API at all. >> > The >> > DMA API has the idea of buffer ownership. Only the owner may access >> > the >> > buffer: >> > >> Are you saying that this scenario does not work ? >> We are taking some liberties with the DMA API, we're more using some >> of its funcs rather than _using_ it ;). >> The question was not whether this was a proper usage of the API, but(Continue reading)
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