linux-kernel - Re: [PATCH v2 1/8] device core: Introduce per-device MSI domain pointer

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Date:	Thu, 15 Jan 2015 14:35:31 -0600
From:	Stuart Yoder <b08248@...il.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Yijing Wang <wangyijing@...wei.com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Subject: Re: [PATCH v2 1/8] device core: Introduce per-device MSI domain pointer

On Thu, Jan 8, 2015 at 11:06 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> As MSI-type features are creeping into non-PCI devices, it is
> starting to make sense to give our struct device some form of
> support for this, by allowing a pointer to an MSI irq domain to
> be set/retrieved.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  include/linux/device.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index fb50673..ec4cee5 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -690,6 +690,7 @@ struct acpi_dev_node {
>   *             along with subsystem-level and driver-level callbacks.
>   * @pins:      For device pin management.
>   *             See Documentation/pinctrl.txt for details.
> + * @msi_domain: The generic MSI domain this device is using.
>   * @numa_node: NUMA node this device is close to.
>   * @dma_mask:  Dma mask (if dma'ble device).
>   * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all
> @@ -750,6 +751,9 @@ struct device {
>         struct dev_pm_info      power;
>         struct dev_pm_domain    *pm_domain;
>
> +#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
> +       struct irq_domain       *msi_domain; /* MSI domain device uses */
> +#endif

This is not a comment on this patch specifically, but a question about other
MSI specific fields that might be needed in struct device.

Currently the generic MSI domain handling has hardcoded assumptions
that devices are PCI-- see the for_each_msi_entry() iterator in msi.h:

  #define dev_to_msi_list(dev)            (&to_pci_dev((dev))->msi_list)

  #define for_each_msi_entry(desc, dev)   \
        list_for_each_entry((desc), dev_to_msi_list((dev)), list)

One approach would be to move the msi_list out of pci_dev and put
it in struct device, so all devices can have an msi_list.

The other approach would be to keep msi_list in a bus specific
device struct, and then dev_to_msi_list() would need to be
implemented as a bus specific callback of some kind.

The above hardcoded PCI assumption isn't going to work.   Wanted to
see if there is any advice in which direction to go.

Thanks,
Stuart Yoder
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