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

[Frank Li <frank.li@nxp.com>]

> -----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;
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> kernel@vger.kernel.org; linux-pci@vger.kernel.org;
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> ntb@lists.linux.dev; Peng Fan <peng.fan@nxp.com>; robh+dt@kernel.org;
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> 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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