[Qemu-devel] Re: [PATCH 38/61] pci: fix pci_default_write_config()

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

On Wed, Sep 30, 2009 at 07:18:14PM +0900, Isaku Yamahata wrote:
> When updated ROM expantion address of header type 0,
> it missed to update mappings.

Can the bugfix be separated from proposed optimization please?
It should be a one-liner.

> By using helper functions this patch also avoids memcpy() and memcmp().

I expect this is all slow-path done during boot, so an extra memcpy
operation can not hurt.

I actually think keeping the original copy around is a good thing,
we probably should put it in PCI structure, so that devices can easily
check whether some value was changed.

For example, in your patch pci_update_mappings is called even if none of
the values are changed, or if memory is disabled, and
you also don't seem to update mappings when memory is enabled/disabled.

> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
> ---
>  hw/pci.c |   11 +++++------
>  hw/pci.h |    9 ++++++++-
>  2 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 757fe7b..2a59667 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -627,20 +627,19 @@ uint32_t pci_default_read_config(PCIDevice *d,
>  
>  void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int l)
>  {
> -    uint8_t orig[PCI_CONFIG_SPACE_SIZE];
>      int i;
>      uint32_t config_size = pcie_config_size(d);
>  
> -    /* not efficient, but simple */
> -    memcpy(orig, d->config, PCI_CONFIG_SPACE_SIZE);
>      for(i = 0; i < l && addr < config_size; val >>= 8, ++i, ++addr) {
>          uint8_t wmask = d->wmask[addr];
>          d->config[addr] = (d->config[addr] & ~wmask) | (val & wmask);
>      }
> -    if (memcmp(orig + PCI_BASE_ADDRESS_0, d->config + PCI_BASE_ADDRESS_0, 24)
> -        || ((orig[PCI_COMMAND] ^ d->config[PCI_COMMAND])
> -            & (PCI_COMMAND_MEMORY | PCI_COMMAND_IO)))
> +
> +    if (pci_config_changed(addr, l,
> +                           PCI_BASE_ADDRESS_0, PCI_BASE_ADDRESS_5 + 4) ||

How can pci_config_changed know whether some value was
actually changed without looking at original and new value?
IMO it's better to keep the original array around,
and use simple memcmp.

> +        pci_config_changed_with_size(addr, l, PCI_ROM_ADDRESS, 4)) {
>          pci_update_mappings(d);
> +    }
>  }
>  
>  static PCIBus *pci_find_bus_from(PCIBus *from, int bus_num)
> diff --git a/hw/pci.h b/hw/pci.h
> index 26c15c5..3327905 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -121,7 +121,12 @@ static inline int pci_bar_is_64bit(const PCIIORegion *r)
>  #define  PCI_HEADER_TYPE_BRIDGE		1
>  #define  PCI_HEADER_TYPE_CARDBUS	2
>  #define  PCI_HEADER_TYPE_MULTI_FUNCTION 0x80
> -#define PCI_BASE_ADDRESS_0	0x10	/* 32 bits */
> +#define PCI_BASE_ADDRESS_0      0x10    /* 32 bits */
> +#define PCI_BASE_ADDRESS_1      0x14    /* 32 bits [htype 0,1 only] */
> +#define PCI_BASE_ADDRESS_2      0x18    /* 32 bits [htype 0 only] */
> +#define PCI_BASE_ADDRESS_3      0x1c    /* 32 bits */
> +#define PCI_BASE_ADDRESS_4      0x20    /* 32 bits */
> +#define PCI_BASE_ADDRESS_5      0x24    /* 32 bits */
>  #define PCI_PRIMARY_BUS		0x18	/* Primary bus number */
>  #define PCI_SECONDARY_BUS	0x19	/* Secondary bus number */
>  #define PCI_SEC_STATUS		0x1e	/* Secondary status register, only bit 14 used */
> @@ -141,7 +146,9 @@ static inline int pci_bar_is_64bit(const PCIIORegion *r)
>  #define PCI_SUBVENDOR_ID        0x2c    /* obsolete, use PCI_SUBSYSTEM_VENDOR_ID */
>  #define PCI_SUBDEVICE_ID        0x2e    /* obsolete, use PCI_SUBSYSTEM_ID */
>  
> +#define PCI_ROM_ADDRESS         0x30    /* Bits 31..11 are address, 10..1 reserved */
>  #define  PCI_ROM_ADDRESS_ENABLE 0x01
> +#define PCI_ROM_ADDRESS_MASK    (~0x7ffUL)
>  
>  /* Bits in the PCI Status Register (PCI 2.3 spec) */
>  #define PCI_STATUS_RESERVED1	0x007
> -- 
> 1.6.0.2