Re: [Qemu-devel] [PATCH v3 2/3] pci: add QEMU-specific PCI capability structure

[Marcel Apfelbaum <marcel@redhat.com>]

On 31/07/2017 17:00, Michael S. Tsirkin wrote:
> On Sat, Jul 29, 2017 at 02:34:31AM +0300, Aleksandr Bezzubikov wrote:
>> On PCI init PCI bridge devices may need some
>> extra info about bus number to reserve, IO, memory and
>> prefetchable memory limits. QEMU can provide this
>> with special vendor-specific PCI capability.
>>
>> This capability is intended to be used only
>> for Red Hat PCI bridges, i.e. QEMU cooperation.
>>
>> Signed-off-by: Aleksandr Bezzubikov <zuban32s@gmail.com>
>> ---
>>   src/fw/dev-pci.h | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 62 insertions(+)
>>   create mode 100644 src/fw/dev-pci.h
>>
>> diff --git a/src/fw/dev-pci.h b/src/fw/dev-pci.h
>> new file mode 100644
>> index 0000000..fbd49ed
>> --- /dev/null
>> +++ b/src/fw/dev-pci.h
>> @@ -0,0 +1,62 @@
>> +#ifndef _PCI_CAP_H
>> +#define _PCI_CAP_H
>> +
>> +#include "types.h"
>> +
>> +/*
>> +
>> +QEMU-specific vendor(Red Hat)-specific capability.
>> +It's intended to provide some hints for firmware to init PCI devices.
>> +
>> +Its is shown below:
>> +
>> +Header:
>> +
>> +u8 id;       Standard PCI Capability Header field
>> +u8 next;     Standard PCI Capability Header field
>> +u8 len;      Standard PCI Capability Header field
>> +u8 type;     Red Hat vendor-specific capability type:
>> +               now only REDHAT_QEMU_CAP 1 exists
>> +Data:
>> +
>> +u16 non_prefetchable_16;     non-prefetchable memory limit
>> +
>> +u8 bus_res;  minimum bus number to reserve;
>> +             this is necessary for PCI Express Root Ports
>> +             to support PCIE-to-PCI bridge hotplug
>> +
>> +u8 io_8;     IO limit in case of 8-bit limit value
>> +u32 io_32;   IO limit in case of 16-bit limit value
>> +             io_8 and io_16 are mutually exclusive, in other words,
>> +             they can't be non-zero simultaneously
>> +
>> +u32 prefetchable_32;         non-prefetchable memory limit
>> +                             in case of 32-bit limit value
>> +u64 prefetchable_64;         non-prefetchable memory limit
>> +                             in case of 64-bit limit value
>> +                             prefetachable_32 and prefetchable_64 are
>> +                             mutually exclusive, in other words,
>> +                             they can't be non-zero simultaneously
>> +If any field in Data section is 0,
>> +it means that such kind of reservation
>> +is not needed.
>

Hi Michael,

> We also want a way to say "no hint for this type".
> 
> One way to achive this would be to have instead multiple
> vendor specific capabilities, one for each of
> bus#/io/mem/prefetch. 0 would mean do not reserve anything,
> absence of capability would mean "no info, up to firmware".
> 

First version of the series was implemented exactly like you propose,
however Gerd preferred only one capability with multiple fields.

I personally like the simplicity of vendor cap per io/mem/bus,
even if it is on the expense of the limited PCI Config space.

We need a consensus here :)

Thanks,
Marcel

> 
>> +
>> +*/
>> +
>> +/* Offset of vendor-specific capability type field */
>> +#define PCI_CAP_VNDR_SPEC_TYPE  3
> 
> This is a QEMU specific thing. Please name it as such.
> 
>> +
>> +/* List of valid Red Hat vendor-specific capability types */
>> +#define REDHAT_CAP_TYPE_QEMU    1
>> +
>> +
>> +/* Offsets of QEMU capability fields */
>> +#define QEMU_PCI_CAP_NON_PREF   4
>> +#define QEMU_PCI_CAP_BUS_RES    6
>> +#define QEMU_PCI_CAP_IO_8       7
>> +#define QEMU_PCI_CAP_IO_32      8
>> +#define QEMU_PCI_CAP_PREF_32    12
>> +#define QEMU_PCI_CAP_PREF_64    16
>> +#define QEMU_PCI_CAP_SIZE       24
>> +
>> +#endif /* _PCI_CAP_H */
>> -- 
>> 2.7.4