| Message ID | 20220324014836.19149-2-Sergey.Semin@baikalelectronics.ru |
|---|---|
| State | New |
| Headers | show |
| Series | dmaengine: dw-edma: Add RP/EP local DMA controllers support | expand |
On Thu, Mar 24, 2022 at 07:00:04PM +0530, Manivannan Sadhasivam wrote: > On Thu, Mar 24, 2022 at 04:48:12AM +0300, Serge Semin wrote: > > The dma_slave_config.direction field usage in the DW eDMA driver has been > > introduced in the commit bd96f1b2f43a ("dmaengine: dw-edma: support local > > dma device transfer semantics"). Mainly the change introduced there was > > correct (indeed DEV_TO_MEM means using RD-channel and MEM_TO_DEV - > > WR-channel for the case of having eDMA accessed locally from > > CPU/Application side), but providing an additional > > MEM_TO_MEM/DEV_TO_DEV-based semantics was quite redundant if not to say > > potentially harmful (when it comes to removing the denoted field). First > > of all since the dma_slave_config.direction field has been marked as > > obsolete (see [1] and the structure dc [2]) and will be discarded in > > future, using it especially in a non-standard way is discouraged. Secondly > > in accordance with the commit denoted above the default > > dw_edma_device_transfer() semantics has been changed despite what it's > > message said. So claiming that the method was left backward compatible was > > wrong. > > > > Anyway let's fix the problems denoted above and simplify the > > dw_edma_device_transfer() method by dropping the parsing of the > > DMA-channel direction field. Instead of having that implicit > > dma_slave_config.direction field semantic we can use the recently added > > DW_EDMA_CHIP_LOCAL flag to distinguish between the local and remote DW > > eDMA setups thus preserving both cases support. In addition to that an > > ASCII-figure has been added to clarify the complication out. > > > > [1] Documentation/driver-api/dmaengine/provider.rst > > [2] include/linux/dmaengine.h: dma_slave_config.direction > > > > Co-developed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> > > > > --- > > > > In accordance with agreement with Frank and Manivannan this patch is > > supposed to be moved to the series: > > Link: https://lore.kernel.org/dmaengine/20220310192457.3090-1-Frank.Li@nxp.com/ > > in place of the patch: > > [PATCH v5 6/9] dmaengine: dw-edma: Don't rely on the deprecated "direction" member > > Link: https://lore.kernel.org/dmaengine/20220310192457.3090-7-Frank.Li@nxp.com/ > > --- > > drivers/dma/dw-edma/dw-edma-core.c | 49 +++++++++++++++++++++--------- > > 1 file changed, 34 insertions(+), 15 deletions(-) > > > > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c > > index 5be8a5944714..e9e32ed74aa9 100644 > > --- a/drivers/dma/dw-edma/dw-edma-core.c > > +++ b/drivers/dma/dw-edma/dw-edma-core.c > > @@ -339,21 +339,40 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer) > > if (!chan->configured) > > return NULL; > > > > - switch (chan->config.direction) { > > - case DMA_DEV_TO_MEM: /* local DMA */ > > - if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_READ) > > - break; > > - return NULL; > > - case DMA_MEM_TO_DEV: /* local DMA */ > > - if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_WRITE) > > - break; > > - return NULL; > > - default: /* remote DMA */ > > - if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_READ) > > - break; > > - if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_WRITE) > > - break; > > - return NULL; > > + /* > > + * Local Root Port/End-point Remote End-point > > + * +-----------------------+ PCIe bus +----------------------+ > > + * | | +-+ | | > > + * | DEV_TO_MEM Rx Ch <----+ +---+ Tx Ch DEV_TO_MEM | > > + * | | | | | | > > + * | MEM_TO_DEV Tx Ch +----+ +---> Rx Ch MEM_TO_DEV | > > + * | | +-+ | | > > + * +-----------------------+ +----------------------+ > > + * > > + * 1. Normal logic: > > + * If eDMA is embedded into the DW PCIe RP/EP and controlled from the > > + * CPU/Application side, the Rx channel (EDMA_DIR_READ) will be used > > + * for the device read operations (DEV_TO_MEM) and the Tx channel > > + * (EDMA_DIR_WRITE) - for the write operations (MEM_TO_DEV). > > + * > > + * 2. Inverted logic: > > + * If eDMA is embedded into a Remote PCIe EP and is controlled by the > > + * MWr/MRd TLPs sent from the CPU's PCIe host controller, the Tx > > + * channel (EDMA_DIR_WRITE) will be used for the device read operations > > + * (DEV_TO_MEM) and the Rx channel (EDMA_DIR_READ) - for the write > > + * operations (MEM_TO_DEV). > > + * > > + * It is the client driver responsibility to choose a proper channel > > + * for the DMA transfers. > > + */ > > I think it'd be good to document this using some form in "enum dw_edma_dir" > declaration. Well, I'd rather leave the comment here. The dw_edma_dir enumeration only defines the actual device channel direction, while the actual semantics is determined by the PCIe device residence/configuration (local + host/end-point, remote + end-point) and is reflected in the data transfer function - dw_edma_device_transfer(). So as I see it the comment is more suitable to be left here in the place where the semantic is actually implemented. -Sergey > > Thanks, > Mani > > > + if (chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) { > > + if ((chan->dir == EDMA_DIR_READ && dir != DMA_DEV_TO_MEM) || > > + (chan->dir == EDMA_DIR_WRITE && dir != DMA_MEM_TO_DEV)) > > + return NULL; > > + } else { > > + if ((chan->dir == EDMA_DIR_WRITE && dir != DMA_DEV_TO_MEM) || > > + (chan->dir == EDMA_DIR_READ && dir != DMA_MEM_TO_DEV)) > > + return NULL; > > } > > > > if (xfer->type == EDMA_XFER_CYCLIC) { > > -- > > 2.35.1 > >
diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c index 5be8a5944714..e9e32ed74aa9 100644 --- a/drivers/dma/dw-edma/dw-edma-core.c +++ b/drivers/dma/dw-edma/dw-edma-core.c @@ -339,21 +339,40 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer) if (!chan->configured) return NULL; - switch (chan->config.direction) { - case DMA_DEV_TO_MEM: /* local DMA */ - if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_READ) - break; - return NULL; - case DMA_MEM_TO_DEV: /* local DMA */ - if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_WRITE) - break; - return NULL; - default: /* remote DMA */ - if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_READ) - break; - if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_WRITE) - break; - return NULL; + /* + * Local Root Port/End-point Remote End-point + * +-----------------------+ PCIe bus +----------------------+ + * | | +-+ | | + * | DEV_TO_MEM Rx Ch <----+ +---+ Tx Ch DEV_TO_MEM | + * | | | | | | + * | MEM_TO_DEV Tx Ch +----+ +---> Rx Ch MEM_TO_DEV | + * | | +-+ | | + * +-----------------------+ +----------------------+ + * + * 1. Normal logic: + * If eDMA is embedded into the DW PCIe RP/EP and controlled from the + * CPU/Application side, the Rx channel (EDMA_DIR_READ) will be used + * for the device read operations (DEV_TO_MEM) and the Tx channel + * (EDMA_DIR_WRITE) - for the write operations (MEM_TO_DEV). + * + * 2. Inverted logic: + * If eDMA is embedded into a Remote PCIe EP and is controlled by the + * MWr/MRd TLPs sent from the CPU's PCIe host controller, the Tx + * channel (EDMA_DIR_WRITE) will be used for the device read operations + * (DEV_TO_MEM) and the Rx channel (EDMA_DIR_READ) - for the write + * operations (MEM_TO_DEV). + * + * It is the client driver responsibility to choose a proper channel + * for the DMA transfers. + */ + if (chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) { + if ((chan->dir == EDMA_DIR_READ && dir != DMA_DEV_TO_MEM) || + (chan->dir == EDMA_DIR_WRITE && dir != DMA_MEM_TO_DEV)) + return NULL; + } else { + if ((chan->dir == EDMA_DIR_WRITE && dir != DMA_DEV_TO_MEM) || + (chan->dir == EDMA_DIR_READ && dir != DMA_MEM_TO_DEV)) + return NULL; } if (xfer->type == EDMA_XFER_CYCLIC) {
The dma_slave_config.direction field usage in the DW eDMA driver has been introduced in the commit bd96f1b2f43a ("dmaengine: dw-edma: support local dma device transfer semantics"). Mainly the change introduced there was correct (indeed DEV_TO_MEM means using RD-channel and MEM_TO_DEV - WR-channel for the case of having eDMA accessed locally from CPU/Application side), but providing an additional MEM_TO_MEM/DEV_TO_DEV-based semantics was quite redundant if not to say potentially harmful (when it comes to removing the denoted field). First of all since the dma_slave_config.direction field has been marked as obsolete (see [1] and the structure dc [2]) and will be discarded in future, using it especially in a non-standard way is discouraged. Secondly in accordance with the commit denoted above the default dw_edma_device_transfer() semantics has been changed despite what it's message said. So claiming that the method was left backward compatible was wrong. Anyway let's fix the problems denoted above and simplify the dw_edma_device_transfer() method by dropping the parsing of the DMA-channel direction field. Instead of having that implicit dma_slave_config.direction field semantic we can use the recently added DW_EDMA_CHIP_LOCAL flag to distinguish between the local and remote DW eDMA setups thus preserving both cases support. In addition to that an ASCII-figure has been added to clarify the complication out. [1] Documentation/driver-api/dmaengine/provider.rst [2] include/linux/dmaengine.h: dma_slave_config.direction Co-developed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> --- In accordance with agreement with Frank and Manivannan this patch is supposed to be moved to the series: Link: https://lore.kernel.org/dmaengine/20220310192457.3090-1-Frank.Li@nxp.com/ in place of the patch: [PATCH v5 6/9] dmaengine: dw-edma: Don't rely on the deprecated "direction" member Link: https://lore.kernel.org/dmaengine/20220310192457.3090-7-Frank.Li@nxp.com/ --- drivers/dma/dw-edma/dw-edma-core.c | 49 +++++++++++++++++++++--------- 1 file changed, 34 insertions(+), 15 deletions(-)