Re: [PATCH v13 1/2] PCI: endpoint: pci-epf-vntb: change doorbell register offset calc mathod

Manivannan Sadhasivam
2022-11-24T09:19:37Z

On Thu, Nov 24, 2022 at 12:50:35AM -0500, Frank Li wrote:
> In drivers/ntb/hw/epf/ntb_hw_epf.c
> ntb_epf_peer_db_set()
> {
> ...
> db_offset = readl(ndev->ctrl_reg + NTB_EPF_DB_OFFSET(interrupt_num));
> writel(db_data, ndev->db_reg + (db_entry_size * interrupt_num) +
> db_offset);
> ...
> }
>
> The door register offset's formular is
> offset = db_entry_size * interrupt_num + db_offset[interrupt_number]

You did not mention the DB BAR here. Without that, this calculation doesn't
make sense.

>
> Previous db_entry_size is 4, all db_offset is 0.

s/Previous/Previously

> irq | offset
> --------------
> 0 0
> 1 4
> 2 8
> ...
>
> Change to db_entry_size is 0 and db_offset is 0, 4, 8, ...
> So we can get the same map value between irq and offset. This will be
> convenience for hardware doorbell register memory map.
>

In your irq-imx-mu-msi.c driver, the msi_address is calculated as:

```
u64 addr = msi_data->msiir_addr + 4 * data->hwirq;
```

So the MSI addresses itself are of 4 bytes width. So the offsets will be
separated by 8 bytes like, 0, 8, 16,... and this won't match the MSI addresses
as they are 4 bytes apart.

So you want to change the offset to 0, 4, 8,... by zeroing db_entry_size,
right?

> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> drivers/pci/endpoint/functions/pci-epf-vntb.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 04698e7995a5..0d744975f815 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -461,11 +461,11 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
> ctrl->num_mws = ntb->num_mws;
> ntb->spad_size = spad_size;
>
> - ctrl->db_entry_size = sizeof(u32);
> + ctrl->db_entry_size = 0;
>
> for (i = 0; i < ntb->db_count; i++) {
> ntb->reg->db_data[i] = 1 + i;
> - ntb->reg->db_offset[i] = 0;
> + ntb->reg->db_offset[i] = sizeof(u32) * i;

If my above understanding is correct, then you could just reassign
"db_entry_size" in epf_ntb_epc_msi_init().

Thanks,
Mani

> }
>
> return 0;
> --
> 2.34.1
>

--
மணிவண்ணன் சதாசிவம்