Re: [PATCH v2 2/3] dmaengine: dw-edma: Enable Chan Separation via VSEC

On Fri, Jul 31, 2026 at 04:22:22PM +0530, Verma, Devendra wrote:
>
>
> On 28-Jul-26 21:03, Frank Li wrote:
> > On Tue, Jul 28, 2026 at 02:47:43PM +0530, Devendra K Verma wrote:
> > > As per, 'Designware Cores PCI Express DM Controller - Reference
> > > Manual', section 3.2.34.3, VSEC for DEVICE INFORMATION supports
> > > the channel separation mechanisms. Basically, the HDMA IP allows
> > > the user to configure the separation between DMA channel
> > > registers and retrieve it via the VSEC capability mentioned
> > > above.
> > >
> > > HDMA IP supports the channel register space separation from
> > > 256B to 32KB. Default supported size is 256B.
> > >
> > > Signed-off-by: Devendra K Verma <[email protected]>
> > > ---
> > > Changes in v1:
> > >     o Modified dw_edma_get_ch_sep_sz() as per review comment.
> > >       The function now supports ch_sep_sz up to 32KB.
> > >     o Updated to description to reflect the supported channel
> > >       separation sizes.
> > >     o Introduced the CPM6 specific macro for VSEC cap.
> > > ---
> > >   drivers/dma/dw-edma/dw-edma-pcie.c | 21 ++++++++++++++++++---
> > >   1 file changed, 18 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/dma/dw-edma/dw-edma-pcie.c b/drivers/dma/dw-edma/dw-edma-pcie.c
> > > index ec5e057a0f11..d0f209082878 100644
> > > --- a/drivers/dma/dw-edma/dw-edma-pcie.c
> > > +++ b/drivers/dma/dw-edma/dw-edma-pcie.c
> > > @@ -31,8 +31,11 @@
> > >
> > >   #define DW_PCIE_XILINX_VSEC_DMA_ID		0x6
> > >   #define DW_PCIE_XILINX_VSEC_ID			0x20
> > > -#define DW_PCIE_XILINX_VSEC_DMA_BAR		GENMASK(10, 8)
> > >   #define DW_PCIE_XILINX_VSEC_DMA_MAP		GENMASK(2, 0)
> > > +#define DW_PCIE_XILINX_VSEC_DMA_BAR		GENMASK(10, 8)
> > > +/* AMD CPM6 (Xilinx) supported cap */
> > > +#define DW_PCIE_XILINX_CPM6_VSEC_CH_SEP		GENMASK(18, 16)
> > > +
> > >   #define DW_PCIE_XILINX_VSEC_DMA_WR_CH		GENMASK(9, 0)
> > >   #define DW_PCIE_XILINX_VSEC_DMA_RD_CH		GENMASK(25, 16)
> > >
> > > @@ -73,6 +76,7 @@ struct dw_edma_pcie_data {
> > >   	u16				wr_ch_cnt;
> > >   	u16				rd_ch_cnt;
> > >   	u64				devmem_phys_off;
> > > +	u32				ch_sep_sz;
> >
> > ch_space_sz?
>
> In the document, Designware Cores PCI Express controller Reference
> Manual, it widely referred as channel separation and ch_sep

which version? I only find "Register Wire Channel seperation" at 6.21a
Feb 2025.

Frank

> has been used so in order to keep the relevance with the document,
> I chose it to be ch_sep_sz. The other name used is chaddr_space but
> it is not used widely as the ch_sep.
> With your suggestion, it can be infered to be same but relevance with
> the document may not be established.
>
> In the past, a similar discussion we had for choosing the non_ll
> naming and chose this as it mentioned and has relevance with the
> document.
>
> Reference
> https://lore.kernel.org/all/20251223162842.GA4022246@bhelgaas/
>
> >
> > >   };
> > >
> > >   static const struct dw_edma_pcie_data snps_edda_data = {
> > > @@ -127,7 +131,7 @@ static const struct dw_edma_pcie_data xilinx_mdb_data = {
> > >   };
> > >
> > >   static const struct dw_edma_pcie_data xilinx_cpm6_dma_data = {
> > > -	/* MDB registers location */
> > > +	/* CPM6 registers location */
> > >   	.rg.bar				= BAR_0,
> > >   	.rg.off				= SZ_4K,	/*  4 Kbytes */
> > >   	.rg.sz				= SZ_8K,	/*  8 Kbytes */
> > > @@ -189,6 +193,13 @@ static int dw_edma_pcie_irq_vector(struct device *dev, unsigned int nr)
> > >   	return pci_irq_vector(to_pci_dev(dev), nr);
> > >   }
> > >
> > > +static u32 dw_edma_get_ch_sep_sz(u32 ch_sep_val)
> > > +{
> > > +	if (ch_sep_val > 0 && ch_sep_val <= 7)
> > > +		return 256 << ch_sep_val;
> > > +	return 256;
> > > +}
> > > +
> > >   static u64 dw_edma_pcie_address(struct device *dev, phys_addr_t cpu_addr)
> > >   {
> > >   	struct pci_dev *pdev = to_pci_dev(dev);
> > > @@ -279,6 +290,10 @@ static void dw_edma_pcie_get_xilinx_dma_data(struct pci_dev *pdev,
> > >   	pdata->mf = map;
> > >   	pdata->rg.bar = FIELD_GET(DW_PCIE_XILINX_VSEC_DMA_BAR, val);
> > >
> > > +	if (pdev->device == PCI_DEVICE_ID_XILINX_B00F)
> > > +		pdata->ch_sep_sz = dw_edma_get_ch_sep_sz(FIELD_GET(DW_PCIE_XILINX_CPM6_VSEC_CH_SEP,
> > > +								   val));
> > > +
> > >   	pci_read_config_dword(pdev, vsec + 0xc, &val);
> > >   	pdata->wr_ch_cnt = min(pdata->wr_ch_cnt,
> > >   			       FIELD_GET(DW_PCIE_XILINX_VSEC_DMA_WR_CH, val));
> > > @@ -324,9 +339,9 @@ static int dw_edma_pcie_probe(struct pci_dev *pdev,
> > >   	struct dw_edma_pcie_data *pdata = (void *)pid->driver_data;
> > >   	struct device *dev = &pdev->dev;
> > >   	struct dw_edma_chip *chip;
> > > +	bool non_ll = false;
> > >   	int err, nr_irqs;
> > >   	int i, mask;
> > > -	bool non_ll = false;
> >
> > unnecesary change
> >
> > Frank
>
> Yes, it is an unncessary change. It was introduced by me in some patch
> series and wanted to maintain the revers x-mas order that's why posted
> it. The declration order looks in the patch after this change.
> Please suggest is it OK to include changes like this or it is kind of
> extra scrutiny for the reviewers? I will make the change accordingly
> in next patch.
>
>
> >
> > >
> > >   	if (!pdata)
> > >   		return -ENODEV;
> > > --
> > > 2.43.0
> > >
>