linux-kernel - Re: [PATCH V3 1/3] ACPI, PCI IRQ: add PCI

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Message-ID: <CAJZ5v0iiU-1JwAows+WbE9v3pjYi9cRHDwtDEDBuCUjWk=o=KA@mail.gmail.com>
Date:   Sat, 15 Oct 2016 14:39:59 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>, ravikanth.nalla@....com,
        Ondrej Zary <linux@...nbow-software.org>,
        Timur Tabi <timur@...eaurora.org>,
        Christopher Covington <cov@...eaurora.org>,
        Jon Masters <jcm@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Andy Gross <agross@...eaurora.org>,
        linux-arm-msm@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, wim@....tudelft.nl,
        Len Brown <lenb@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 1/3] ACPI, PCI IRQ: add PCI_USING penalty for ISA interrupts

On Sat, Oct 15, 2016 at 6:31 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
> The change introduced in commit 103544d86976 ("ACPI,PCI,IRQ: reduce
> resource requirements") removed PCI_USING penalty from
> acpi_pci_link_allocate function as there is no longer a fixed size penalty
> array for both PCI interrupts greater than 16.
>
> The array size has been reduced to 16 and array name got prefixed as ISA
> since it only is accountable for the ISA interrupts.
>
> The original change in commit 103544d86976 ("ACPI,PCI,IRQ: reduce
> resource requirements") removed penalty assignment in the code for PCI
> thinking that we will add the penalty later in acpi_irq_pci_sharing_penalty
> function.

I'd write the above this way:

"Commit 103544d86976 (ACPI,PCI,IRQ: reduce resource requirements)
dropped the PCI_USING penalty from acpi_pci_link_allocate() with the
assumption that the penalty will be added later in
acpi_irq_pci_sharing_penalty()."

This conveys essentially the same information (up to some irrelevant
bits), but in a clearer way IMO.

>
> However, this function only gets called if the IRQ number is greater than
> 16 and acpi_irq_get_penalty function gets called before ACPI start in
> acpi_isa_irq_available and acpi_penalize_isa_irq functions. We can't rely
> on iterating the link list.

"However, acpi_irq_pci_sharing_penalty() is only called for IRQ
numbers above 15.  Moreover, acpi_irq_get_penalty() is invoked by
acpi_isa_irq_available() and acpi_penalize_isa_irq() before the ACPI
initialization and the PCI interrupt links list is not ready at that
point, so it cannot be relied on when computing the penalty."

>
> We need to add the PCI_USING penalty for ISA interrupts too if the link is
> in use and matches our ISA IRQ number.

"For this reason, the PCI_USING penalty has to be added in
acpi_pci_link_allocate() directly if the link has been enabled
successfully and the IRQ number is within the ISA range."

IIUC

>
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/acpi/pci_link.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
> index c983bf7..a212709 100644
> --- a/drivers/acpi/pci_link.c
> +++ b/drivers/acpi/pci_link.c
> @@ -619,6 +619,10 @@ static int acpi_pci_link_allocate(struct acpi_pci_link *link)
>                             acpi_device_bid(link->device));
>                 return -ENODEV;
>         } else {
> +               if (link->irq.active < ACPI_MAX_ISA_IRQS)
> +                       acpi_isa_irq_penalty[link->irq.active] +=
> +                               PIRQ_PENALTY_PCI_USING;
> +

There's no need to break the line here and I would put the above after
the printk().

Or even after the whole "else" branch (which is unnecessary, but let's
limit changes in this patch).

>                 printk(KERN_WARNING PREFIX "%s [%s] enabled at IRQ %d\n",
>                        acpi_device_name(link->device),
>                        acpi_device_bid(link->device), link->irq.active);
> --

Thanks,
Rafael