[Qemu-devel] Re: [PATCH v5 04/14] pci/bridge: fix pci_bridge_reset()

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

On Tue, Oct 19, 2010 at 06:06:31PM +0900, Isaku Yamahata wrote:
> The default value of base/limit registers aren't specified in the spec.
> So pci_bridge_reset() shouldn't touch them.
> Instead, introduced two functions to reset those registers in a way
> of typical implementation. zero base/limit registers or disable forwarding.
> They will be used later.
> 
> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
> ---

I have some second thoughts:

1. pci_bridge_reset is used in several devices and I have no idea what
the reset change will do there, how do real devices behave or whether
guests depend on a specific behaviour.  It seems harmless to leave the
current implementation in place, and simply add
pci_bridge_disable_base_limit which devices can call after
pci_bridge_reset.

2.  _zero and _disable describe what function does already,
so we should drop _reset from function name.
Thus we only get 1 new function, pci_bridge_disable_base_limit.

> Changes v4 -> v5:
> - drop the lines in pci_bridge_reset()
> - introduced two functions to reset base/limit registers.
> ---
>  hw/pci_bridge.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++-------
>  hw/pci_bridge.h |    2 +
>  2 files changed, 51 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/pci_bridge.c b/hw/pci_bridge.c
> index 638e3b3..de75e6a 100644
> --- a/hw/pci_bridge.c
> +++ b/hw/pci_bridge.c
> @@ -151,6 +151,46 @@ void pci_bridge_write_config(PCIDevice *d,
>      }
>  }
>  
> +void pci_bridge_reset_zero_base_limit(PCIDevice *dev)
> +{
> +    uint8_t *conf = dev->config;
> +
> +    pci_byte_test_and_clear_mask(conf + PCI_IO_BASE,
> +                                 PCI_IO_RANGE_MASK & 0xff);
> +    pci_byte_test_and_clear_mask(conf + PCI_IO_LIMIT,
> +                                 PCI_IO_RANGE_MASK & 0xff);
> +    pci_word_test_and_clear_mask(conf + PCI_MEMORY_BASE,
> +                                 PCI_MEMORY_RANGE_MASK & 0xffff);
> +    pci_word_test_and_clear_mask(conf + PCI_MEMORY_LIMIT,
> +                                 PCI_MEMORY_RANGE_MASK & 0xffff);
> +    pci_word_test_and_clear_mask(conf + PCI_PREF_MEMORY_BASE,
> +                                 PCI_PREF_RANGE_MASK & 0xffff);
> +    pci_word_test_and_clear_mask(conf + PCI_PREF_MEMORY_LIMIT,
> +                                 PCI_PREF_RANGE_MASK & 0xffff);
> +    pci_set_word(conf + PCI_PREF_BASE_UPPER32, 0);
> +    pci_set_word(conf + PCI_PREF_LIMIT_UPPER32, 0);
> +}
> +
> +void pci_bridge_reset_disable_base_limit(PCIDevice *dev)
> +{
> +    uint8_t *conf = dev->config;
> +
> +    pci_byte_test_and_set_mask(conf + PCI_IO_BASE,
> +                               PCI_IO_RANGE_MASK & 0xff);
> +    pci_byte_test_and_clear_mask(conf + PCI_IO_LIMIT,
> +                                 PCI_IO_RANGE_MASK & 0xff);
> +    pci_word_test_and_set_mask(conf + PCI_MEMORY_BASE,
> +                               PCI_MEMORY_RANGE_MASK & 0xffff);
> +    pci_word_test_and_clear_mask(conf + PCI_MEMORY_LIMIT,
> +                                 PCI_MEMORY_RANGE_MASK & 0xffff);
> +    pci_word_test_and_set_mask(conf + PCI_PREF_MEMORY_BASE,
> +                               PCI_PREF_RANGE_MASK & 0xffff);
> +    pci_word_test_and_clear_mask(conf + PCI_PREF_MEMORY_LIMIT,
> +                                 PCI_PREF_RANGE_MASK & 0xffff);
> +    pci_set_word(conf + PCI_PREF_BASE_UPPER32, 0);
> +    pci_set_word(conf + PCI_PREF_LIMIT_UPPER32, 0);
> +}
> +
>  /* reset bridge specific configuration registers */
>  void pci_bridge_reset_reg(PCIDevice *dev)
>  {
> @@ -161,14 +201,15 @@ void pci_bridge_reset_reg(PCIDevice *dev)
>      conf[PCI_SUBORDINATE_BUS] = 0;
>      conf[PCI_SEC_LATENCY_TIMER] = 0;
>  
> -    conf[PCI_IO_BASE] = 0;
> -    conf[PCI_IO_LIMIT] = 0;
> -    pci_set_word(conf + PCI_MEMORY_BASE, 0);
> -    pci_set_word(conf + PCI_MEMORY_LIMIT, 0);
> -    pci_set_word(conf + PCI_PREF_MEMORY_BASE, 0);
> -    pci_set_word(conf + PCI_PREF_MEMORY_LIMIT, 0);
> -    pci_set_word(conf + PCI_PREF_BASE_UPPER32, 0);
> -    pci_set_word(conf + PCI_PREF_LIMIT_UPPER32, 0);
> +    /*
> +     * the default values for base/limit registers aren't specified
> +     * in the PCI-to-PCI-bridge spec. So we don't thouch them here.
> +     * Each implementation can override it.
> +     * typical implementation does
> +     * - zero registers: pci_bridge_reset_zer_base_limit()
> +     * or
> +     * - disable forwarding: pci_bridge_reset_disable_base_limit()
> +     */
>  
>      pci_set_word(conf + PCI_BRIDGE_CONTROL, 0);
>  }
> diff --git a/hw/pci_bridge.h b/hw/pci_bridge.h
> index f6fade0..2359684 100644
> --- a/hw/pci_bridge.h
> +++ b/hw/pci_bridge.h
> @@ -39,6 +39,8 @@ pcibus_t pci_bridge_get_limit(const PCIDevice *bridge, uint8_t type);
>  
>  void pci_bridge_write_config(PCIDevice *d,
>                               uint32_t address, uint32_t val, int len);
> +void pci_bridge_reset_zero_base_limit(PCIDevice *dev);
> +void pci_bridge_reset_disable_base_limit(PCIDevice *dev);
>  void pci_bridge_reset_reg(PCIDevice *dev);
>  void pci_bridge_reset(DeviceState *qdev);
>  
> -- 
> 1.7.1.1