Re: [PATCH v2 1/6] pci: implement power state

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Nov 11, 2021 at 02:08:54PM +0100, Gerd Hoffmann wrote:
> This allows to power off pci devices.  In "off" state the devices will
> not be visible.  No pci config space access, no pci bar access, no dma.
> 
> Default state is "on", so this patch (alone) should not change behavior.
> 
> Use case:  Allows hotplug controllers implement slot power.  Hotplug
> controllers doing so should set the inital power state for devices in
> the ->plug callback.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  include/hw/pci/pci.h |  2 ++
>  hw/pci/pci.c         | 25 +++++++++++++++++++++++--
>  hw/pci/pci_host.c    |  6 ++++--
>  3 files changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> index 5c4016b9954a..e7cdf2d5ec5d 100644
> --- a/include/hw/pci/pci.h
> +++ b/include/hw/pci/pci.h
> @@ -268,6 +268,7 @@ typedef struct PCIReqIDCache PCIReqIDCache;
>  struct PCIDevice {
>      DeviceState qdev;
>      bool partially_hotplugged;
> +    bool has_power;
>  
>      /* PCI config space */
>      uint8_t *config;
> @@ -908,5 +909,6 @@ extern const VMStateDescription vmstate_pci_device;
>  }
>  
>  MSIMessage pci_get_msi_message(PCIDevice *dev, int vector);
> +void pci_set_power(PCIDevice *pci_dev, bool state);
>  
>  #endif
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 4a84e478cef5..e5993c1ef52b 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -1380,6 +1380,9 @@ static void pci_update_mappings(PCIDevice *d)
>              continue;
>  
>          new_addr = pci_bar_address(d, i, r->type, r->size);
> +        if (!d->has_power) {
> +            new_addr = PCI_BAR_UNMAPPED;
> +        }
>  
>          /* This bar isn't changed */
>          if (new_addr == r->addr)

I am a bit confused about why this is necessary.
When power is removed device is reset, does not
this disable device memory automatically?


> @@ -1464,8 +1467,8 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val_in, int
>      if (range_covers_byte(addr, l, PCI_COMMAND)) {
>          pci_update_irq_disabled(d, was_irq_disabled);
>          memory_region_set_enabled(&d->bus_master_enable_region,
> -                                  pci_get_word(d->config + PCI_COMMAND)
> -                                    & PCI_COMMAND_MASTER);
> +                                  (pci_get_word(d->config + PCI_COMMAND)
> +                                   & PCI_COMMAND_MASTER) && d->has_power);
>      }
>  
>      msi_write_config(d, addr, val_in, l);
> @@ -2182,6 +2185,8 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
>          pci_qdev_unrealize(DEVICE(pci_dev));
>          return;
>      }
> +
> +    pci_set_power(pci_dev, true);
>  }
>  
>  PCIDevice *pci_new_multifunction(int devfn, bool multifunction,
> @@ -2853,6 +2858,22 @@ MSIMessage pci_get_msi_message(PCIDevice *dev, int vector)
>      return msg;
>  }
>  
> +void pci_set_power(PCIDevice *d, bool state)
> +{
> +    if (d->has_power == state) {
> +        return;
> +    }
> +
> +    d->has_power = state;
> +    pci_update_mappings(d);
> +    memory_region_set_enabled(&d->bus_master_enable_region,
> +                              (pci_get_word(d->config + PCI_COMMAND)
> +                               & PCI_COMMAND_MASTER) && d->has_power);
> +    if (!d->has_power) {
> +        pci_device_reset(d);
> +    }
> +}
> +
>  static const TypeInfo pci_device_type_info = {
>      .name = TYPE_PCI_DEVICE,
>      .parent = TYPE_DEVICE,
> diff --git a/hw/pci/pci_host.c b/hw/pci/pci_host.c
> index cf02f0d6a501..7beafd40a8e9 100644
> --- a/hw/pci/pci_host.c
> +++ b/hw/pci/pci_host.c
> @@ -74,7 +74,8 @@ void pci_host_config_write_common(PCIDevice *pci_dev, uint32_t addr,
>      /* non-zero functions are only exposed when function 0 is present,
>       * allowing direct removal of unexposed functions.
>       */
> -    if (pci_dev->qdev.hotplugged && !pci_get_function_0(pci_dev)) {
> +    if ((pci_dev->qdev.hotplugged && !pci_get_function_0(pci_dev)) ||
> +        !pci_dev->has_power) {
>          return;
>      }
>  
> @@ -97,7 +98,8 @@ uint32_t pci_host_config_read_common(PCIDevice *pci_dev, uint32_t addr,
>      /* non-zero functions are only exposed when function 0 is present,
>       * allowing direct removal of unexposed functions.
>       */
> -    if (pci_dev->qdev.hotplugged && !pci_get_function_0(pci_dev)) {
> +    if ((pci_dev->qdev.hotplugged && !pci_get_function_0(pci_dev)) ||
> +        !pci_dev->has_power) {
>          return ~0x0;
>      }
>  
> -- 
> 2.33.1