Re: [PATCH 01/15] pcie: Set default and supported MaxReadReq to 512

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

On Thu, Oct 07, 2021 at 06:23:52PM +0200, Lukasz Maniak wrote:
> From: Knut Omang <knut.omang@oracle.com>
> 
> Make the default PCI Express Capability for PCIe devices set
> MaxReadReq to 512.

code says 256

> Tyipcal modern devices people would want to


typo

> emulate or simulate would want this. The previous value would
> cause warnings from the root port driver on some kernels.


which specifically?

> 
> Signed-off-by: Knut Omang <knuto@ifi.uio.no>

we can't make changes like this unconditionally, this will
break migration across versions.
Pls tie this to a machine version.

Thanks!
> ---
>  hw/pci/pcie.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 6e95d82903..c1a12f3744 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -62,8 +62,9 @@ pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
>       * Functions conforming to the ECN, PCI Express Base
>       * Specification, Revision 1.1., or subsequent PCI Express Base
>       * Specification revisions.
> +     *  + set max payload size to 256, which seems to be a common value
>       */
> -    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER);
> +    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER | (0x1 & PCI_EXP_DEVCAP_PAYLOAD));
>  
>      pci_set_long(exp_cap + PCI_EXP_LNKCAP,
>                   (port << PCI_EXP_LNKCAP_PN_SHIFT) |
> @@ -179,6 +180,8 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset,
>      pci_set_long(exp_cap + PCI_EXP_DEVCAP2,
>                   PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);
>  
> +    pci_set_word(exp_cap + PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_READRQ_256B);
> +
>      pci_set_word(dev->wmask + pos + PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_EETLPPB);
>  
>      if (dev->cap_present & QEMU_PCIE_EXTCAP_INIT) {
> -- 
> 2.25.1