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

Frank Li
2022-11-24T17:49:40Z

> -----Original Message-----
> From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Sent: Thursday, November 24, 2022 3:19 AM
> To: Frank Li <frank.li@nxp.com>
> Cc: lpieralisi@kernel.org; Aisheng Dong <aisheng.dong@nxp.com>;
> bhelgaas@google.com; devicetree@vger.kernel.org; festevam@gmail.com;
> imx@lists.linux.dev; jdmason@kudzu.us; kernel@pengutronix.de;
> kishon@ti.com; krzysztof.kozlowski+dt@linaro.org; kw@linux.com; linux-
> arm-kernel@lists.infradead.org; dl-linux-imx <linux-imx@nxp.com>; linux-
> kernel@vger.kernel.org; linux-pci@vger.kernel.org;
> lorenzo.pieralisi@arm.com; lznuaa@gmail.com; maz@kernel.org;
> ntb@lists.linux.dev; Peng Fan <peng.fan@nxp.com>; robh+dt@kernel.org;
> s.hauer@pengutronix.de; shawnguo@kernel.org; tglx@linutronix.de
> Subject: [EXT] Re: [PATCH v13 1/2] PCI: endpoint: pci-epf-vntb: change
> doorbell register offset calc mathod
>
> Caution: EXT Email
>
> 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.

Doorbell register offset should means Base on DB BAR.
How about "The formula of door register offset refer to DB BAR"?

>
> >
> > 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.

Addr is absolute physical IO address, which increased by 4. But it doesn't matter.
It should be okay if range is between 2^32.

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

I want to directly using db_offset[irq] value as offset. It will be simple.

I am not sure why ntb_hw_epf.c use below formular.
"Db_offset[irq] + irq * db_entry_size"

Db_entry_size = 0 will be simple, all offset will be controlled by db_offset[]

You can save db_offset[] as 0, 4, 8... or 0, 8, 16 as needs.

>
> > 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().

Yes, that's one method.
I want to use one method to calc db offset for both software polling
and MSI. So overall logic should be simple.

Frank Li

>
> Thanks,
> Mani
>
> > }
> >
> > return 0;
> > --
> > 2.34.1
> >
>
> --
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