Re: [Patch Part3 V1 17/22] pci, ACPI, iommu: enhance pci_root to support DMAR device hotplug

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, Apr 22, 2014 at 03:07:28PM +0800, Jiang Liu wrote:
> Finally enhance pci_root driver to support DMAR device hotplug when
> hot-plugging PCI host bridges.
> 
> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
> ---
>  drivers/acpi/pci_root.c |   16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index d388f13d48b4..aa8f549869f3 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -33,6 +33,7 @@
>  #include <linux/pci.h>
>  #include <linux/pci-acpi.h>
>  #include <linux/pci-aspm.h>
> +#include <linux/dmar.h>
>  #include <linux/acpi.h>
>  #include <linux/slab.h>
>  #include <acpi/apei.h>	/* for acpi_hest_init() */
> @@ -511,6 +512,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
>  	struct acpi_pci_root *root;
>  	acpi_handle handle = device->handle;
>  	int no_aspm = 0, clear_aspm = 0;
> +	bool hotadd = (system_state != SYSTEM_BOOTING);
>  
>  	root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
>  	if (!root)
> @@ -557,6 +559,11 @@ static int acpi_pci_root_add(struct acpi_device *device,
>  	strcpy(acpi_device_class(device), ACPI_PCI_ROOT_CLASS);
>  	device->driver_data = root;
>  
> +	if (hotadd && dmar_device_hotplug(handle, true)) {

Apparently "dmar_device_hotplug(handle, true)" means "add a DMAR device,"
and "dmar_device_hotplug(device->handle, false)" means "remove a DMAR
device."  I'm not really a fan of interfaces where one of the arguments
selects between two completely different actions, because it's harder for a
casual reader to see what's going on.

I see how it simplifies your implementation a little bit, but I think it's
more important to simplify for the reader.

Bjorn