Re: [EXT] Re: [PATCH v13 2/2] PCI: endpoint: pci-epf-vntb: using platform MSI as doorbell

From: Manivannan Sadhasivam
Date: Thu Nov 24 2022 - 13:46:18 EST

On Thu, Nov 24, 2022 at 06:03:40PM +0000, Frank Li wrote:
>
>
> > -----Original Message-----
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > Sent: Thursday, November 24, 2022 3:00 AM
> > To: Frank Li <frank.li@xxxxxxx>
> > Cc: lpieralisi@xxxxxxxxxx; Aisheng Dong <aisheng.dong@xxxxxxx>;
> > bhelgaas@xxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> > imx@xxxxxxxxxxxxxxx; jdmason@xxxxxxxx; kernel@xxxxxxxxxxxxxx;
> > kishon@xxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; kw@xxxxxxxxx; linux-
> > arm-kernel@xxxxxxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; linux-
> > kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > lorenzo.pieralisi@xxxxxxx; lznuaa@xxxxxxxxx; maz@xxxxxxxxxx;
> > ntb@xxxxxxxxxxxxxxx; Peng Fan <peng.fan@xxxxxxx>; robh+dt@xxxxxxxxxx;
> > s.hauer@xxxxxxxxxxxxxx; shawnguo@xxxxxxxxxx; tglx@xxxxxxxxxxxxx
> > Subject: [EXT] Re: [PATCH v13 2/2] PCI: endpoint: pci-epf-vntb: using platform
> > MSI as doorbell
> >
> > Caution: EXT Email
> >
> > On Thu, Nov 24, 2022 at 12:50:36AM -0500, Frank Li wrote:
> > > ┌────────────┐ ┌───────────────
> > ────────────────────┐ ┌─────────
> > ───────┐
> > > │ │ │ │ │ │
> > > │ │ │ PCI Endpoint │ │ PCI Host │
> > > │ │ │ │ │ │
> > > │ │◄──┤ 1.platform_msi_domain_alloc_irqs()│ │
> > │
> > > │ │ │ │ │ │
> > > │ MSI ├──►│ 2.write_msi_msg() ├──►├─BAR<n>
> > │
> > > │ Controller │ │ update doorbell register address│ │ │
> > > │ │ │ for BAR │ │ │
> > > │ │ │ │ │ 3. Write BAR<n>│
> > > │ │◄──┼──────────────────────
> > ─────────────┼───┤ │
> > > │ │ │ │ │ │
> > > │ ├──►│ 4.Irq Handle │ │ │
> > > │ │ │ │ │ │
> > > │ │ │ │ │ │
> > > └────────────┘ └───────────────
> > ────────────────────┘ └─────────
> > ───────┘
> > >
> >
> > There are at least couple of BAR regions used in this patch but they were not
> > mentioned in the above diagram.
>
> This patch just affected one BAR regions. Do you like "BAR[DB]"?
>
> Do you want to me draw other BARs, which used by this function?
>

It'd be good to just mention DB BAR.

> >
> > The subject should be:
> >
> > "PCI: endpoint: pci-epf-vntb: Use EP MSI controller to handle DB from host"
> >
> > > Using platform MSI interrupt controller as endpoint(EP)'s doorbell.
> > >
> >
> > Above line is not needed.
> >
> > > The memory assigned for BAR region by the PCI host is mapped to the
> >
> > Which BAR? (BAR 1 aka. DB BAR)? There are multiple BAR regions exposed by
> > this function driver.
> >
> > > message address of platform msi interrupt controller in PCI Endpoint.
> >
> > s/msi/MSI. Also, use either Endpoint or EP, pick one but not both.
> >
> > > Such that, whenever the PCI host writes to the BAR region, it will
> > > trigger an IRQ in the EP.
> > >
> > > Basic working follow as
> >
> > "work flow is"?
> >
> > > 1. EP function driver call platform_msi_domain_alloc_irqs() alloc a
> >
> > pci-epf-vntb function driver calls platform_msi_domain_alloc_irqs() to
> > allocate
> > MSI's from the platform MSI controller.
> >
> > > MSI irq from MSI controller with call back function write_msi_msg();
> > > 2. write_msg_msg will config BAR and map to address defined in msi_msg;
> >
> > The epf_ntb_write_msi_msg() passed as a callback will write the offset of the
> > MSI controller's MSI address dedicated for each MSI to the doorbell register
> > db_offset and also writes the MSI data to db_data register in the CTRL BAR
> > region.
> >
> > > 3. Host side trigger an IRQ at Endpoint by write to BAR region.
> > >
> >
> > Finally, the host can trigger doorbell by reading the offset of the doorbell
> > from db_offset register and writing the data read from db_data register in
> > CTRL
> > BAR region to the computed address in the DB BAR region.
> >
> > > Add MSI doorbell support for pci-epf-vntb. Query if system has an MSI
> > > controller. Set up doorbell address according to struct msi_msg.
> > >
> > > So PCI host can write this doorbell address to trigger EP side's IRQ.
> > >
> > > If no MSI controller exists, fall back to software polling.
> > >
> >
> > "Add doorbell support to pci-epf-vntb function driver making use of the
> > platform
> > MSI controller. If the MSI controller is not available, fallback to the polling
> > method."
> >
> > Also, please move this paragraph to the beginning of the description.
> >
> > > Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> > > ---
> > > drivers/pci/endpoint/functions/pci-epf-vntb.c | 146 +++++++++++++++---
> > > 1 file changed, 125 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > > index 0d744975f815..f770a068e58c 100644
> > > --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > > +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> > > @@ -44,6 +44,7 @@
> > > #include <linux/pci-epc.h>
> > > #include <linux/pci-epf.h>
> > > #include <linux/ntb.h>
> > > +#include <linux/msi.h>
> > >
> > > static struct workqueue_struct *kpcintb_workqueue;
> > >
> > > @@ -137,11 +138,14 @@ struct epf_ntb {
> > > struct epf_ntb_ctrl *reg;
> > >
> > > u32 *epf_db;
> > > + phys_addr_t epf_db_phys;
> > >
> > > phys_addr_t vpci_mw_phy[MAX_MW];
> > > void __iomem *vpci_mw_addr[MAX_MW];
> > >
> > > struct delayed_work cmd_handler;
> > > +
> > > + int msi_virqbase;
> > > };
> >
> > You should add kernel doc comments for this struct in a separate patch. It
> > will
> > help in understanding the driver better.
> >
> > >
> > > #define to_epf_ntb(epf_group) container_of((epf_group), struct epf_ntb,
> > group)
> > > @@ -256,11 +260,13 @@ static void epf_ntb_cmd_handler(struct
> > work_struct *work)
> > >
> > > ntb = container_of(work, struct epf_ntb, cmd_handler.work);
> > >
> > > - for (i = 1; i < ntb->db_count; i++) {
> > > - if (ntb->epf_db[i]) {
> > > - ntb->db |= 1 << (i - 1);
> > > - ntb_db_event(&ntb->ntb, i);
> > > - ntb->epf_db[i] = 0;
> >
> > A comment here stating that polling is implemented would be better.
> >
> > > + if (!ntb->epf_db_phys) {
> > > + for (i = 1; i < ntb->db_count; i++) {
> > > + if (ntb->epf_db[i]) {
> > > + ntb->db |= 1 << (i - 1);
> > > + ntb_db_event(&ntb->ntb, i);
> > > + ntb->epf_db[i] = 0;
> > > + }
> > > }
> > > }
> > >
> > > @@ -518,6 +524,28 @@ static int epf_ntb_configure_interrupt(struct
> > epf_ntb *ntb)
> > > return 0;
> > > }
> > >
> > > +static int epf_ntb_db_size(struct epf_ntb *ntb)
> > > +{
> > > + const struct pci_epc_features *epc_features;
> > > + size_t size = sizeof(u32) * ntb->db_count;
> > > + u32 align;
> > > +
> > > + epc_features = pci_epc_get_features(ntb->epf->epc,
> > > + ntb->epf->func_no,
> > > + ntb->epf->vfunc_no);
> > > + align = epc_features->align;
> > > +
> > > + if (size < 128)
> >
> > Shouldn't this be (size > 128)?
>
> This is one coming from pci-epf-ntb.c.
> Not sure there are some EP hardware have such limitation.
>

I'm not sure if that is correct though. drivers/ntb/hw/epf/ntb_hw_epf.c sets
the upper limit to 32 (NTB_EPF_MAX_DB_COUNT + 1) DBs, in that case the size
cannot go beyond 128.

Thanks,
Mani
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