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Date: Wed, 13 Jul 2022 18:28:53 +0000
From: Frank Li <frank.li@....com>
To: Marc Zyngier <maz@...nel.org>
CC: "tglx@...utronix.de" <tglx@...utronix.de>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"krzysztof.kozlowski+dt@...aro.org"
<krzysztof.kozlowski+dt@...aro.org>,
"shawnguo@...nel.org" <shawnguo@...nel.org>,
"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
"kw@...ux.com" <kw@...ux.com>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
Peng Fan <peng.fan@....com>,
Aisheng Dong <aisheng.dong@....com>,
"jdmason@...zu.us" <jdmason@...zu.us>,
"kernel@...gutronix.de" <kernel@...gutronix.de>,
"festevam@...il.com" <festevam@...il.com>,
dl-linux-imx <linux-imx@....com>,
"kishon@...com" <kishon@...com>,
"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
"ntb@...ts.linux.dev" <ntb@...ts.linux.dev>
Subject: RE: [EXT] Re: [PATCH 1/3] irqchip: imx mu worked as msi controller
> -----Original Message-----
> From: Frank Li
> Sent: Saturday, July 9, 2022 10:23 AM
> To: Marc Zyngier <maz@...nel.org>
> Cc: tglx@...utronix.de; robh+dt@...nel.org;
> krzysztof.kozlowski+dt@...aro.org; shawnguo@...nel.org;
> s.hauer@...gutronix.de; kw@...ux.com; bhelgaas@...gle.com; linux-
> kernel@...r.kernel.org; devicetree@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; linux-pci@...r.kernel.org; Peng Fan
> <peng.fan@....com>; Aisheng Dong <aisheng.dong@....com>;
> jdmason@...zu.us; kernel@...gutronix.de; festevam@...il.com; dl-linux-
> imx <linux-imx@....com>; kishon@...com; lorenzo.pieralisi@....com;
> ntb@...ts.linux.dev
> Subject: RE: [EXT] Re: [PATCH 1/3] irqchip: imx mu worked as msi controller
>
>
>
> > -----Original Message-----
> > From: Marc Zyngier <maz@...nel.org>
> > Sent: Saturday, July 9, 2022 3:16 AM
> > To: Frank Li <frank.li@....com>
> > Cc: tglx@...utronix.de; robh+dt@...nel.org;
> > krzysztof.kozlowski+dt@...aro.org; shawnguo@...nel.org;
> > s.hauer@...gutronix.de; kw@...ux.com; bhelgaas@...gle.com; linux-
> > kernel@...r.kernel.org; devicetree@...r.kernel.org; linux-arm-
> > kernel@...ts.infradead.org; linux-pci@...r.kernel.org; Peng Fan
> > <peng.fan@....com>; Aisheng Dong <aisheng.dong@....com>;
> > jdmason@...zu.us; kernel@...gutronix.de; festevam@...il.com; dl-
> linux-
> > imx <linux-imx@....com>; kishon@...com; lorenzo.pieralisi@....com;
> > ntb@...ts.linux.dev
> > Subject: Re: [EXT] Re: [PATCH 1/3] irqchip: imx mu worked as msi controller
> >
> > Caution: EXT Email
> >
> > On Fri, 08 Jul 2022 17:26:33 +0100,
> > Frank Li <frank.li@....com> wrote:
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Marc Zyngier <maz@...nel.org>
> > > > Sent: Friday, July 8, 2022 3:59 AM
> > > > To: Frank Li <frank.li@....com>
> > > > Cc: tglx@...utronix.de; robh+dt@...nel.org;
> > > > krzysztof.kozlowski+dt@...aro.org; shawnguo@...nel.org;
> > > > s.hauer@...gutronix.de; kw@...ux.com; bhelgaas@...gle.com; linux-
> > > > kernel@...r.kernel.org; devicetree@...r.kernel.org; linux-arm-
> > > > kernel@...ts.infradead.org; linux-pci@...r.kernel.org; Peng Fan
> > > > <peng.fan@....com>; Aisheng Dong <aisheng.dong@....com>;
> > > > jdmason@...zu.us; kernel@...gutronix.de; festevam@...il.com; dl-
> > linux-
> > > > imx <linux-imx@....com>; kishon@...com; lorenzo.pieralisi@....com;
> > > > ntb@...ts.linux.dev
> > > > Subject: [EXT] Re: [PATCH 1/3] irqchip: imx mu worked as msi controller
> > > >
> > > > Caution: EXT Email
> > > >
> > > > On Thu, 07 Jul 2022 22:02:36 +0100,
> > > > Frank Li <Frank.Li@....com> wrote:
> > > > >
> > > > > MU support generate irq by write data to a register.
> > > > > This patch make mu worked as msi controller.
> > > > > So MU can do doorbell by using standard msi api.
> > > > >
> > > > > Signed-off-by: Frank Li <Frank.Li@....com>
> > > > > ---
> > > > > drivers/irqchip/Kconfig | 7 +
> > > > > drivers/irqchip/Makefile | 1 +
> > > > > drivers/irqchip/irq-imx-mu-msi.c | 490
> > > > +++++++++++++++++++++++++++++++
> > > > > 3 files changed, 498 insertions(+)
> > > > > create mode 100644 drivers/irqchip/irq-imx-mu-msi.c
> > > > >
> >
> > [...]
> >
> > > > > +static void imx_mu_msi_mask_irq(struct irq_data *data)
> > > > > +{
> > > > > + struct imx_mu_msi *msi_data = irq_data_get_irq_chip_data(data-
> > > > >parent_data);
> > > > > +
> > > > > + pci_msi_mask_irq(data);
> > > >
> > > > What is this? Below, you create a platform MSI domain. Either you
> > > > support PCI, and you create a PCI/MSI domain (and the above may
> make
> > > > sense), or you are doing platform MSI, and the above is non-sense.
> > >
> > > [Frank Li] You are right. This work as platform msi. Needn't call
> pci_msi_irq()
> >
> > OK, hold that thought and see below.
> >
> > > > > +static int imx_mu_msi_domain_irq_alloc(struct irq_domain *domain,
> > > > > + unsigned int virq,
> > > > > + unsigned int nr_irqs,
> > > > > + void *args)
> > > > > +{
> > > > > + struct imx_mu_msi *msi_data = domain->host_data;
> > > > > + msi_alloc_info_t *info = args;
> > > > > + int pos, err = 0;
> > > > > +
> > > > > + pm_runtime_get_sync(&msi_data->pdev->dev);
> > > >
> > > > The core code already deals with runtime PM. What prevents it from
> > > > working, other than the fact you don't populate the device in the
> > > > top-level domain?
> > >
> > > [Frank Li] Do you means power domain or irq domain?
> >
> > IRQ domain. See irq_domain_set_pm_device() and how PM is used on
> > interrupt request.
> >
> > [...]
> >
> > > > > +static void imx_mu_msi_domain_irq_free(struct irq_domain
> *domain,
> > > > > + unsigned int virq, unsigned int nr_irqs)
> > > > > +{
> > > > > + struct irq_data *d = irq_domain_get_irq_data(domain, virq);
> > > > > + struct imx_mu_msi *msi_data = irq_data_get_irq_chip_data(d);
> > > > > + int pos;
> > > > > +
> > > > > + pos = d->hwirq;
> > > > > + if (pos < 0 || pos >= msi_data->irqs_num) {
> > > > > + pr_err("failed to teardown msi. Invalid hwirq %d\n", pos);
> > > > > + return;
> > > > > + }
> > > >
> > > > How can this happen?
> > >
> > > I just copy from irq-ls-scfg-msi.c
> >
> > I wish you didn't do that.
> >
> > > It should be impossible happen if everything work as expected.
> >
> > Then it should go.
> >
> > [...]
> >
> > > > > +static const struct imx_mu_dcfg imx_mu_cfg_imx6sx = {
> > > > > + .xTR = 0x0,
> > > > > + .xRR = 0x10,
> > > > > + .xSR = {0x20, 0x20, 0x20, 0x20},
> > > > > + .xCR = {0x24, 0x24, 0x24, 0x24},
> > > > > +};
> > > > > +
> > > > > +static const struct imx_mu_dcfg imx_mu_cfg_imx7ulp = {
> > > > > + .xTR = 0x20,
> > > > > + .xRR = 0x40,
> > > > > + .xSR = {0x60, 0x60, 0x60, 0x60},
> > > > > + .xCR = {0x64, 0x64, 0x64, 0x64},
> > > > > +};
> > > > > +
> > > > > +static const struct imx_mu_dcfg imx_mu_cfg_imx8ulp = {
> > > > > + .type = IMX_MU_V2,
> > > > > + .xTR = 0x200,
> > > > > + .xRR = 0x280,
> > > > > + .xSR = {0xC, 0x118, 0x124, 0x12C},
> > > > > + .xCR = {0x110, 0x114, 0x120, 0x128},
> > > > > +};
> > > > > +
> > > > > +static const struct imx_mu_dcfg imx_mu_cfg_imx8ulp_s4 = {
> > > > > + .type = IMX_MU_V2 | IMX_MU_V2_S4,
> > > > > + .xTR = 0x200,
> > > > > + .xRR = 0x280,
> > > > > + .xSR = {0xC, 0x118, 0x124, 0x12C},
> > > > > + .xCR = {0x110, 0x114, 0x120, 0x128},
> > > > > +};
> > > >
> > > > What are these? We really don't need more magic numbers.
> > >
> > > It is register offset. The difference version MU hardware's
> > > register map is difference.
> >
> > Then please document what this is, what the various registers are, and
> > correctly set type everywhere.
> >
> > [...]
> >
> > > > If that's hardcoded, why do we need an extra variable? I also question
> > > > the usefulness of this driver if the HW can only deal with *4* MSIs...
> > > > This looks a bit like a joke.
> > >
> > > MU don't really MSI controller. Each MU have 4 channel.
> > > I.MX have several MU units.
> >
> > Then is it really useful to model that as a MSI controller? This
> > smells of a mailbox controller to me instead.
>
> MU already have driver as mailbox controller. But mailbox interface can't
> Match PCI-EP requirement.
>
> ┌───────┐ ┌──────────┐
> │ │ │ │
> │ │ │ PCI Host │
> │ │ │ │
> │ │ │ │
> │ │ │ Bar0 │
> │ PCI │ │ Bar1 │
> │ Func │ │ Bar2 │
> │ │ │ Bar3 │
> │ │ │ Bar4 │
> │ ├─────────►│ │
> └───────┘ MSI └──────────┘
>
> Many PCI controllers provided Endpoint functions.
> Generally PCI endpoint is hardware, which is not running a rich OS, like linux.
>
> But Linux also supports endpoint functions. PCI Host write bar<n> space like
> write to memory. The EP side can't know memory changed by the Host driver.
>
> PCI Spec has not defined a standard method to do that. Only define MSI<x>
> to let
> EP notified RC status change.
>
> The basic idea is to trigger an irq when PCI RC writes to a memory
> address. That's
> what MSI controller provided. EP drivers just need to request a platform MSI
> interrupt,
> struct msi_msg *msg will pass down a memory address and data. EP driver
> will
> map such memory address to one of PCI bar<n>. Host just writes such an
> address to
> trigger EP side irq.
>
> > And I really worry that
> > this device doesn't correctly preserve the ordering between a device
> > doing DMA and generating an interrupt to indicate completion of the
> > DMA transaction... Does this block offers such a guarantee?
>
> According to PCI memory model, the sequence of write is the ordered.
> PCI host write data to DDR, then write data to MSI (MU)'s register are
> ordered.
>
> PCI->AXI bridge will guarantee the order, otherwise it will block memory
> model.
>
> >
> > > PCI EP driver need an address as doorbell, so PCI RC side can write
> > > This address to trigger irq. Ideally, it use GIC-ITS. But our i.MX chip
> > > Have not ITS support yet now. So we can use MU as simple MSI
> controller.
> >
> > Is that an integrated EP on the same SoC? Or are you talking of two
> > SoCs connected over PCIe?
>
> Two Socs connected over PCIe.
>
> > Also, you explicitly said that this was
> > *not* a PCI/MSI controller. So what is this all about?
>
> I think real MSI controller works as
> 1. Write data to address to trigger irq. Data is DID | irq_number.
> 2. MSI controller can distribute difference irq to difference core.
> 3. There are status bit, which match irq_number. If DID| <0> and DID | <1>
> write
> To address at same time, both <0> an <1> irq can be handled.
> 4. other features ..
>
> MU is not designed as MSI controller at hardware.
> But if we limit irq_number to 1, MU can work as MSI controller although only
> provide 4 irq numbers.
>
> For NTB using case, it is enough. Because i.MX have not gic-its, I have to use
> MU as MSI controller.
> So PCIe EP can use it to improve transfer latency. Without it, PCI ep driver
> have to using polling to check
> Status, delay will be bigger than 5ms. With msi, transfer delay will < 1ms.
>
> I will put all background information at cover letter at next version.
Marc: Do you agree on the overall design? If yes, I will respin patches.
Best regards
Frank Li
>
> >
> > [...]
> >
> > > > > +static int imx_mu_msi_remove(struct platform_device *pdev)
> > > > > +{
> > > > > + struct imx_mu_msi *msi_data = platform_get_drvdata(pdev);
> > > > > +
> > > > > + imx_mu_msi_teardown_hwirq(msi_data);
> > > > > +
> > > > > + irq_domain_remove(msi_data->msi_domain);
> > > > > + irq_domain_remove(msi_data->parent);
> > > >
> > > > How do you ensure that no device is still holding interrupts? Let me
> > > > give you a hint: you can't. So removing an interrupt controller module
> > > > should not be possible.
> > >
> > > [Frank Li] I agree. But there are many *_remove under irqchip.
> >
> > That doesn't make it right.
> >
> > Thanks,
> >
> > M.
> >
> > --
> > Without deviation from the norm, progress is not possible.
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