[EXT] Re: [PATCH v13 2/2] PCI: endpoint: pci-epf-vntb: using platform MSI as doorbell
Frank Li
frank.li at nxp.com
Thu Nov 24 10:03:40 PST 2022
> -----Original Message-----
> From: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
> Sent: Thursday, November 24, 2022 3:00 AM
> To: Frank Li <frank.li at nxp.com>
> Cc: lpieralisi at kernel.org; Aisheng Dong <aisheng.dong at nxp.com>;
> bhelgaas at google.com; devicetree at vger.kernel.org; festevam at gmail.com;
> imx at lists.linux.dev; jdmason at kudzu.us; kernel at pengutronix.de;
> kishon at ti.com; krzysztof.kozlowski+dt at linaro.org; kw at linux.com; linux-
> arm-kernel at lists.infradead.org; dl-linux-imx <linux-imx at nxp.com>; linux-
> kernel at vger.kernel.org; linux-pci at vger.kernel.org;
> lorenzo.pieralisi at arm.com; lznuaa at gmail.com; maz at kernel.org;
> ntb at lists.linux.dev; Peng Fan <peng.fan at nxp.com>; robh+dt at kernel.org;
> s.hauer at pengutronix.de; shawnguo at kernel.org; tglx at linutronix.de
> 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?
>
> 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 at nxp.com>
> > ---
> > 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.
>
> > + size = 128;
> > +
> > + if (align)
> > + size = ALIGN(size, align);
> > + else
> > + size = roundup_pow_of_two(size);
> > +
> > + return size;
> > +}
> > +
> > /**
> > * epf_ntb_db_bar_init() - Configure Doorbell window BARs
> > * @ntb: NTB device that facilitates communication between HOST and
> VHOST
> > @@ -539,27 +567,26 @@ static int epf_ntb_db_bar_init(struct epf_ntb
> *ntb)
> > ntb->epf->func_no,
> > ntb->epf->vfunc_no);
> > align = epc_features->align;
> > -
> > - if (size < 128)
> > - size = 128;
> > -
> > - if (align)
> > - size = ALIGN(size, align);
> > - else
> > - size = roundup_pow_of_two(size);
> > + size = epf_ntb_db_size(ntb);
> >
> > barno = ntb->epf_ntb_bar[BAR_DB];
> > + epf_bar = &ntb->epf->bar[barno];
> >
> > - mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, align, 0);
> > - if (!mw_addr) {
> > - dev_err(dev, "Failed to allocate OB address\n");
> > - return -ENOMEM;
> > + if (ntb->epf_db_phys) {
> > + mw_addr = NULL;
> > + epf_bar->phys_addr = ntb->epf_db_phys;
> > + epf_bar->barno = barno;
> > + epf_bar->size = size;
> > + } else {
> > + mw_addr = pci_epf_alloc_space(ntb->epf, size, barno, align, 0);
> > + if (!mw_addr) {
> > + dev_err(dev, "Failed to allocate doorbell address\n");
> > + return -ENOMEM;
> > + }
> > }
> >
> > ntb->epf_db = mw_addr;
> >
> > - epf_bar = &ntb->epf->bar[barno];
> > -
> > ret = pci_epc_set_bar(ntb->epf->epc, ntb->epf->func_no, ntb->epf-
> >vfunc_no, epf_bar);
> > if (ret) {
> > dev_err(dev, "Doorbell BAR set failed\n");
> > @@ -728,6 +755,82 @@ static int epf_ntb_init_epc_bar(struct epf_ntb
> *ntb)
> > return 0;
> > }
> >
> > +static irqreturn_t epf_ntb_interrupt_handler(int irq, void *data)
>
> Shouldn't this function also be guarded?
>
> > +{
> > + struct epf_ntb *ntb = data;
> > + int index;
> > +
> > + index = irq - ntb->msi_virqbase;
> > + ntb->db |= 1 << (index - 1);
> > + ntb_db_event(&ntb->ntb, index);
> > +
> > + return IRQ_HANDLED;
> > +}
> > +
> > +#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
>
> It'd be better to use the relevant commit description as a comment here.
>
> > +static void epf_ntb_write_msi_msg(struct msi_desc *desc, struct msi_msg
> *msg)
> > +{
> > + struct epf_ntb *ntb = dev_get_drvdata(desc->dev);
> > + struct epf_ntb_ctrl *reg = ntb->reg;
> > + int size = epf_ntb_db_size(ntb);
> > + u64 addr;
> > +
> > + addr = msg->address_hi;
> > + addr <<= 32;
> > + addr |= msg->address_lo;
> > +
> > + reg->db_data[desc->msi_index] = msg->data;
> > +
>
> A comment stating that the base address to be used as the DB BAR is set here
> would be useful too.
>
> > + if (!desc->msi_index)
> > + ntb->epf_db_phys = round_down(addr, size);
> > +
> > + reg->db_offset[desc->msi_index] = addr - ntb->epf_db_phys;
> > +}
> > +
> > +static void epf_ntb_epc_msi_init(struct epf_ntb *ntb)
> > +{
> > + struct device *dev = &ntb->epf->dev;
> > + struct irq_domain *domain;
> > + int virq;
> > + int ret;
> > + int i;
> > +
> > + domain = dev_get_msi_domain(ntb->epf->epc->dev.parent);
> > + if (!domain)
> > + return;
> > +
> > + dev_set_msi_domain(dev, domain);
> > +
> > + if (platform_msi_domain_alloc_irqs(&ntb->epf->dev,
> > + ntb->db_count,
> > + epf_ntb_write_msi_msg)) {
>
> Please wrap above two in a single line till 100 column limit.
>
> > + dev_err(dev, "Can't allocate MSI, falling back to polling mode\n");
>
> This should be dev_dbg().
>
> > + return;
> > + }
> > + dev_dbg(dev, "Using MSI as doorbell\n");
> > +
> > + for (i = 0; i < ntb->db_count; i++) {
> > + virq = msi_get_virq(dev, i);
> > + ret = devm_request_irq(dev, virq,
> > + epf_ntb_interrupt_handler, 0,
> > + "pci_epf_vntb", ntb);
> > +
> > + if (ret) {
> > + dev_err(dev, "Failed to request doorbell IRQ! Falling back to
> polling mode");
>
> Again, dev_dbg()
>
> > + ntb->epf_db_phys = 0;
> > + platform_msi_domain_free_irqs(&ntb->epf->dev);
> > + break;
> > + }
> > +
> > + if (!i)
> > + ntb->msi_virqbase = virq; /* msi start virq number */
> > + }
> > +}
> > +#else
>
> Since this is not exposed as an API, just end the ifdef here and...
>
> > +static void epf_ntb_epc_msi_init(struct epf_ntb *ntb)
> > +{
> > +}
> > +#endif /* CONFIG_GENERIC_MSI_IRQ_DOMAIN */
> > /**
> > * epf_ntb_epc_init() - Initialize NTB interface
> > * @ntb: NTB device that facilitates communication between HOST and
> VHOST
> > @@ -1336,14 +1439,15 @@ static int epf_ntb_bind(struct pci_epf *epf)
> > goto err_bar_alloc;
> > }
> >
> > + epf_set_drvdata(epf, ntb);
> > + epf_ntb_epc_msi_init(ntb);
>
> Guard this function instead:
>
> #ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
> epf_ntb_epc_msi_init(ntb);
> #endif
>
> Thanks,
> Mani
>
> > +
> > ret = epf_ntb_epc_init(ntb);
> > if (ret) {
> > dev_err(dev, "Failed to initialize EPC\n");
> > goto err_bar_alloc;
> > }
> >
> > - epf_set_drvdata(epf, ntb);
> > -
> > pci_space[0] = (ntb->vntb_pid << 16) | ntb->vntb_vid;
> > pci_vntb_table[0].vendor = ntb->vntb_vid;
> > pci_vntb_table[0].device = ntb->vntb_pid;
> > --
> > 2.34.1
> >
>
> --
> மணிவண்ணன் சதாசிவம்
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