| Message ID | 1463064854-6719-3-git-send-email-ludovic.desroches@atmel.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
Le 12/05/2016 16:54, Ludovic Desroches a écrit : > Due to the way CUBC register is updated, a double flush is needed to > compute an accurate residue. First flush aim is to get data from the DMA > FIFO and second one ensures that we won't report data which are not in > memory. > > Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com> > Fixes: e1f7c9eee707 ("dmaengine: at_xdmac: creation of the atmel > eXtended DMA Controller driver") > Cc: stable@vger.kernel.org #v4.1 and later Reviewed-by: Nicolas Ferre <nicolas.ferre@atmel.com> > --- > drivers/dma/at_xdmac.c | 24 +++++++++++++++++++++++- > 1 file changed, 23 insertions(+), 1 deletion(-) > > diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c > index b02494e..75bd662 100644 > --- a/drivers/dma/at_xdmac.c > +++ b/drivers/dma/at_xdmac.c > @@ -1425,7 +1425,16 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie, > residue = desc->xfer_size; > /* > * Flush FIFO: only relevant when the transfer is source peripheral > - * synchronized. > + * synchronized. Flush is needed before reading CUBC because data in > + * the FIFO are not reported by CUBC. Reporting a residue of the > + * transfer length while we have data in FIFO can cause issue. > + * Usecase: atmel USART has a timeout which means I have received > + * characters but there is no more character received for a while. On > + * timeout, it requests the residue. If the data are in the DMA FIFO, > + * we will return a residue of the transfer length. It means no data > + * received. If an application is waiting for these data, it will hang > + * since we won't have another USART timeout without receiving new > + * data. > */ > mask = AT_XDMAC_CC_TYPE | AT_XDMAC_CC_DSYNC; > value = AT_XDMAC_CC_TYPE_PER_TRAN | AT_XDMAC_CC_DSYNC_PER2MEM; > @@ -1481,6 +1490,19 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie, > } > > /* > + * Flush FIFO: only relevant when the transfer is source peripheral > + * synchronized. Another flush is needed here because CUBC is updated > + * when the controller sends the data write command. It can lead to > + * report data that are not written in the memory or the device. The > + * FIFO flush ensures that data are really written. > + */ > + if ((desc->lld.mbr_cfg & mask) == value) { > + at_xdmac_write(atxdmac, AT_XDMAC_GSWF, atchan->mask); > + while (!(at_xdmac_chan_read(atchan, AT_XDMAC_CIS) & AT_XDMAC_CIS_FIS)) > + cpu_relax(); > + } > + > + /* > * Remove size of all microblocks already transferred and the current > * one. Then add the remaining size to transfer of the current > * microblock. >
diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c index b02494e..75bd662 100644 --- a/drivers/dma/at_xdmac.c +++ b/drivers/dma/at_xdmac.c @@ -1425,7 +1425,16 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie, residue = desc->xfer_size; /* * Flush FIFO: only relevant when the transfer is source peripheral - * synchronized. + * synchronized. Flush is needed before reading CUBC because data in + * the FIFO are not reported by CUBC. Reporting a residue of the + * transfer length while we have data in FIFO can cause issue. + * Usecase: atmel USART has a timeout which means I have received + * characters but there is no more character received for a while. On + * timeout, it requests the residue. If the data are in the DMA FIFO, + * we will return a residue of the transfer length. It means no data + * received. If an application is waiting for these data, it will hang + * since we won't have another USART timeout without receiving new + * data. */ mask = AT_XDMAC_CC_TYPE | AT_XDMAC_CC_DSYNC; value = AT_XDMAC_CC_TYPE_PER_TRAN | AT_XDMAC_CC_DSYNC_PER2MEM; @@ -1481,6 +1490,19 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie, } /* + * Flush FIFO: only relevant when the transfer is source peripheral + * synchronized. Another flush is needed here because CUBC is updated + * when the controller sends the data write command. It can lead to + * report data that are not written in the memory or the device. The + * FIFO flush ensures that data are really written. + */ + if ((desc->lld.mbr_cfg & mask) == value) { + at_xdmac_write(atxdmac, AT_XDMAC_GSWF, atchan->mask); + while (!(at_xdmac_chan_read(atchan, AT_XDMAC_CIS) & AT_XDMAC_CIS_FIS)) + cpu_relax(); + } + + /* * Remove size of all microblocks already transferred and the current * one. Then add the remaining size to transfer of the current * microblock.
Due to the way CUBC register is updated, a double flush is needed to compute an accurate residue. First flush aim is to get data from the DMA FIFO and second one ensures that we won't report data which are not in memory. Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com> Fixes: e1f7c9eee707 ("dmaengine: at_xdmac: creation of the atmel eXtended DMA Controller driver") Cc: stable@vger.kernel.org #v4.1 and later --- drivers/dma/at_xdmac.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)