[RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge
Marc Zyngier
marc.zyngier at arm.com
Fri Mar 24 11:47:37 PDT 2017
On 23/03/17 17:03, Mason wrote:
> On 23/03/2017 15:22, Marc Zyngier wrote:
>
>> On 23/03/17 13:05, Mason wrote:
>>
>>> +#define MSI_COUNT 32
>>
>> Is this something that is hardcoded? Unlikely to ever change?
>
> The host bridge actually supports 256 MSIs.
>
> IIUC, what you suggested on IRC is that I support 256 in the driver,
> and only read the status for *enabled* MSIs.
>
> Pseudo-code:
>
> for every 32-bit blob in the enabled bitmap
> if the value is non-zero
> lookup the corresponding status reg
>
> Problem is that a BITMAP is unsigned long (as you point out below).
> So I'm not sure how to iterate 32-bits at a time over the BITMAP.
See my reply in a previous email.
>>> +static void tango_msi_isr(struct irq_desc *desc)
>>> +{
>>> + struct irq_chip *chip = irq_desc_get_chip(desc);
>>> + struct tango_pcie *pcie;
>>> + unsigned long status, virq;
>>> + int pos;
>>> +
>>> + chained_irq_enter(chip, desc);
>>> + pcie = irq_desc_get_handler_data(desc);
>>> +
>>> + status = readl_relaxed(pcie->msi_status);
>>
>> Please use types that unambiguously match that of the MMIO accessor (u32
>> in this case). On a 64bit system, unsigned long is likely to be 64bit.
>> You can assign it to an unsigned long before calling the
>> for_each_set_bit operator.
>
> OK. I'm aware that unsigned long is 64 bits on sane 64b platforms,
> but since extending u32 to u64 would pad with zeros, I didn't expect
> this to be an issue. I will change the code. Note: I copied the
> code from the Altera driver.
This is an issue when your system is 64bit BE, something that is not
that uncommon.
>
>>> + writel_relaxed(status, pcie->msi_status); /* clear IRQs */
>>
>> Why isn't this your irq_ack method instead of open-coding it?
>
> I based my driver on the Altera driver, and I did it like
> I thought they did. I will try fixing my code.
Doesn't make it right, unfortunately. I wish you would try to understand
the API first instead of copy-pasting things (including potential bugs).
>
>>> + for_each_set_bit(pos, &status, MSI_COUNT) {
>>> + virq = irq_find_mapping(pcie->irq_domain, pos);
>>> + if (virq)
>>> + generic_handle_irq(virq);
>>> + else
>>> + pr_err("Unhandled MSI: %d\n", pos);
>>
>> Please rate-limit this.
>
> I'll use pr_err_ratelimited
>
>
>>> +static struct msi_domain_info msi_domain_info = {
>>> + .flags = MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS,
>>
>> No support for MSI-X? Why?
>
> Good question.
> https://en.wikipedia.org/wiki/Message_Signaled_Interrupts#MSI-X
> My controller supports a single doorbell, and only 256 MSIs.
> I thought that meant it didn't support MSI-X.
The "single doorbell" requirement is on the end-point, not on the
controller. Multi-MSI only has a single register for all possible
interrupts, while MSI-X allows one doorbell address per interrupt. In
your case, all interrupts will have the same doorbell address, which is
perfectly fine.
>
>
>>> +static int tango_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
>>> + unsigned int nr_irqs, void *args)
>>> +{
>>> + struct tango_pcie *pcie = domain->host_data;
>>> + int pos, err = 0;
>>> + u32 mask;
>>> +
>>> + if (nr_irqs != 1) /* When does that happen? */
>>> + return -EINVAL;
>>
>> Only if the end-point wants to use Multi-MSI. You don't advertise
>> support for it, so it should never happen.
>
> Should I keep the test or remove it?
Up to you. Some people warn loudly, some other ignore it, you've chosen
a middle ground.
>
>
>>> + mutex_lock(&pcie->lock);
>>> +
>>> + mask = readl_relaxed(pcie->msi_mask);
>>
>> Do you really need to read this from the HW each time you allocate an
>> interrupt? That feels pretty crazy. You're much better off having an
>> in-memory bitmap that will make things more efficient, and avoid the
>> following bug...
>>
>>> + pos = find_first_zero_bit(&mask, MSI_COUNT);
>>
>> ... where using a u32 as a bitmap is a very bad idea (because not the
>> whole world is a 32bit, little endian platform).
>
> I understand your point. This ties in to the ISR discussion.
>
>
>>> + if (pos < MSI_COUNT)
>>> + writel(mask | BIT(pos), pcie->msi_mask);
>>
>> And it would make a lot more sense to move this write (which should be
>> relaxed) to irq_unmask. Also, calling msi_mask for something that is an
>> enable register is a bit counter intuitive.
>
> I don't have as much experience as you.
> I just used the names in the HW documentation.
> I think it is the "mask" (as in bitmap) of enabled MSIs.
> I will change "mask" to "enable".
>
> Are you saying I should not use pci_msi_mask_irq and pci_msi_unmask_irq,
> but register custom implementations? I should still call these in my
> custom functions, right?
You can call both in your own mask/unmask methods. They serve different
purpose (one is at the endpoint level, the other is at the MSI
controller level).
>
>
>>> + else
>>> + err = -ENOSPC;
>>> +
>>> + mutex_unlock(&pcie->lock);
>>> +
>>> + irq_domain_set_info(domain, virq, pos, &tango_msi_chip,
>>> + domain->host_data, handle_simple_irq, NULL, NULL);
>>
>> And here, you're polluting the domain even if you failed to allocate the
>> interrupt.
>
> This bug is 100% mine. Will fix.
Erm. In this file, all bugs are yours! :-)
>
>>> +
>>> + return err;
>>> +}
>>> +
>>> +static void tango_irq_domain_free(struct irq_domain *domain,
>>> + unsigned int virq, unsigned int nr_irqs)
>>> +{
>>> + struct irq_data *d = irq_domain_get_irq_data(domain, virq);
>>> + struct tango_pcie *pcie = irq_data_get_irq_chip_data(d);
>>> + int pos = d->hwirq;
>>> + u32 mask;
>>> +
>>> + mutex_lock(&pcie->lock);
>>> +
>>> + mask = readl(pcie->msi_mask);
>>> + writel(mask & ~BIT(pos), pcie->msi_mask);
>>
>> Same as above, please move this to the irq_unmask method.
>
> This one should be irq_mask, no?
Yes.
>
> Even If I move the MMIO write, it should be done under lock,
> I think. But I don't know in what context irq_unmask will
> be called.
> You said: not mutex, spinlock.
It can be called from interrupt context, so it cannot be a mutex.
>
>
>>> +static int tango_msi_remove(struct platform_device *pdev)
>>> +{
>>> + struct tango_pcie *msi = platform_get_drvdata(pdev);
>>> +
>>> + irq_set_chained_handler(msi->irq, NULL);
>>> + irq_set_handler_data(msi->irq, NULL);
>>> + /* irq_set_chained_handler_and_data(msi->irq, NULL, NULL); instead? */
>
> Can I call irq_set_chained_handler_and_data(msi->irq, NULL, NULL);
> instead of the two calls?
Probably. Reading the code should tell you.
>
>>> + mutex_init(&pcie->lock);
>>> + writel(0, pcie->msi_mask);
>>> +
>>> + /* Why is fwnode for this call? */
>>> + irq_dom = irq_domain_add_linear(NULL, MSI_COUNT, &msi_domain_ops, pcie);
>>
>> Use irq_domain_create_linear, pass the same fwnode.
>
> Will change that.
>
>
>>> + if (!irq_dom) {
>>> + pr_err("Failed to create IRQ domain\n");
>>> + return -ENOMEM;
>>> + }
>>> +
>>> + msi_dom = pci_msi_create_irq_domain(fwnode, &msi_domain_info, irq_dom);
>>> + if (!msi_dom) {
>>> + pr_err("Failed to create MSI domain\n");
>>> + irq_domain_remove(irq_dom);
>>> + return -ENOMEM;
>>> + }
>>> +
>>> + virq = platform_get_irq(pdev, 1);
>>
>> In the absence of a documented binding, it is hard to know if you're
>> doing the right thing.
>
> pcie at 50000000 {
> compatible = "sigma,smp8759-pcie";
> reg = <0x50000000 SZ_64M>, <0x2e000 0x100>;
> device_type = "pci";
> bus-range = <0 63>;
> #size-cells = <2>;
> #address-cells = <3>;
> #interrupt-cells = <1>;
> ranges = <0x02000000 0x0 0x04000000 0x54000000 0x0 SZ_192M>;
> msi-controller;
> /* 54 for misc interrupts, 55 for MSI */
> interrupts = <54 IRQ_TYPE_LEVEL_HIGH>, <55 IRQ_TYPE_LEVEL_HIGH>;
> };
This is not a binding. This is an example from your DT. Look at
Documentation/devicetree/bindings/pci/ for examples of the required
documentation.
>
> Note: I don't have an "interrupt-map" prop because rev1 doesn't support
> legacy PCI interrupts (INTx). But I see the PCI framework wrongly mapping
> intA to my system's interrupt #1, presumably because I am lacking an
> interrupt-map?
Probably. I don't think it is legal not to have an interrupt-map.
>
> Also I find the MSI interrupt number to be high:
>
> # cat /proc/interrupts
> CPU0 CPU1
> 19: 21171 1074 GIC-0 29 Edge twd
> 20: 116 0 irq0 1 Level serial
> 26: 7 0 MSI 0 Edge aerdrv
> 28: 3263 0 MSI 524288 Edge xhci_hcd
>
> 524288 is 0x80000. Was this offset chosen by the intc core?
By the PCI/MSI layer. See pci_msi_domain_calc_hwirq().
Thanks,
M.
--
Jazz is not dead. It just smells funny...
More information about the linux-arm-kernel
mailing list