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

[Frank Li]

On Fri, Jul 31, 2026 at 10:03:10PM +0530, Verma, Devendra wrote:
> On 31-Jul-26 21:04, Frank Li wrote:
> > 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 <devverma@xxxxxxx>
> > > > > ---
> > > > > 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
>
> We have the reference from RM - 6.00a June 2022, following sections:
> - Table 1-4
> - Sec 3.2.34.3, Table 3-276 (VSECDMA_DEVICE_INFORMATION)
> refer to channel separation and describe for HDMA

But this is not register value, the register MACRO defination should follow
spec.

"Channel Separation: Address distance between read and write channels."

helper function dw_edma_get_ch_sep_sz() convert register value to this
field.

The field should use software easy understand/generic term, so reader
can know what's that easily without check spec. Driver need do some
abstract, instead direct copy from hardware.

Frank


>
> -Devendra
>
> >
> > > 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
> > > > >
> > >
>