Re: [PATCH v7 20/26] PNP: Don't reserve BARs for PCI when enabled movable BARs

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jan 29, 2020 at 06:29:31PM +0300, Sergei Miroshnichenko wrote:
> When the Movable BARs feature is supported, the PCI subsystem is able to
> distribute existing BARs and allocate the new ones itself, without need to
> reserve gaps by BIOS.
> 
> CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Signed-off-by: Sergei Miroshnichenko <s.miroshnichenko@yadro.com>
> ---
>  drivers/pnp/system.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pnp/system.c b/drivers/pnp/system.c
> index 6950503741eb..16cd260a609d 100644
> --- a/drivers/pnp/system.c
> +++ b/drivers/pnp/system.c
> @@ -12,6 +12,7 @@
>  #include <linux/device.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> +#include <linux/pci.h>
>  #include <linux/kernel.h>
>  #include <linux/ioport.h>
>  
> @@ -58,6 +59,11 @@ static void reserve_resources_of_dev(struct pnp_dev *dev)
>  	struct resource *res;
>  	int i;
>  
> +#ifdef CONFIG_PCI
> +	if (pci_can_move_bars)
> +		return;
> +#endif

I don't understand this.  The reason this function exists is so we
keep track of the resources consumed by PNP devices and we can keep
from assigning those resources to other things like PCI devices.

Admittedly we currently only do this for PNP0C01 and PNP0C02 devices,
but we really should do it for all PNP devices.

Why does Movable BARs mean that we no longer need this information?
The whole point is that this information is needed *during* PCI
resource allocation, so I don't understand the idea that "because the
PCI subsystem is able to distribute existing BARs and allocate the new
ones itself", we don't need to know about PNP resources to avoid.

>  	for (i = 0; (res = pnp_get_resource(dev, IORESOURCE_IO, i)); i++) {
>  		if (res->flags & IORESOURCE_DISABLED)
>  			continue;
> -- 
> 2.24.1
>