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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Thu, Nov 24, 2022 at 05:49:32PM +0000, Frank Li wrote:
> 
> 
> > -----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"?

"Doobell register offset in DB BAR is calculated using:"

> 
> > 
> > >
> > > 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. 
> 

I think it is better to leave db_entry_size for polling as it is and modify it
for MSI alone.

Thanks,
Mani

> Frank Li
> 
> > 
> > Thanks,
> > Mani
> > 
> > >       }
> > >
> > >       return 0;
> > > --
> > > 2.34.1
> > >
> > 
> > --
> > மணிவண்ணன் சதாசிவம்

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