Re: [PATCH v5 08/11] xen/arm: Enable the existing x86 virtual PCI support for ARM.

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 13 Oct 2021, Jan Beulich wrote:
> On 13.10.2021 16:51, Oleksandr Andrushchenko wrote:
> > On 13.10.21 16:00, Jan Beulich wrote:
> >> On 13.10.2021 10:45, Roger Pau Monné wrote:
> >>> On Wed, Oct 06, 2021 at 06:40:34PM +0100, Rahul Singh wrote:
> >>>> --- /dev/null
> >>>> +++ b/xen/arch/arm/vpci.c
> >>>> @@ -0,0 +1,102 @@
> >>>> +/*
> >>>> + * xen/arch/arm/vpci.c
> >>>> + *
> >>>> + * This program is free software; you can redistribute it and/or modify
> >>>> + * it under the terms of the GNU General Public License as published by
> >>>> + * the Free Software Foundation; either version 2 of the License, or
> >>>> + * (at your option) any later version.
> >>>> + *
> >>>> + * This program is distributed in the hope that it will be useful,
> >>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> >>>> + * GNU General Public License for more details.
> >>>> + */
> >>>> +#include <xen/sched.h>
> >>>> +
> >>>> +#include <asm/mmio.h>
> >>>> +
> >>>> +#define REGISTER_OFFSET(addr)  ( (addr) & 0x00000fff)
> >>>> +
> >>>> +/* Do some sanity checks. */
> >>>> +static bool vpci_mmio_access_allowed(unsigned int reg, unsigned int len)
> >>>> +{
> >>>> +    /* Check access size. */
> >>>> +    if ( len > 8 )
> >>>> +        return false;
> >>>> +
> >>>> +    /* Check that access is size aligned. */
> >>>> +    if ( (reg & (len - 1)) )
> >>>> +        return false;
> >>>> +
> >>>> +    return true;
> >>>> +}
> >>>> +
> >>>> +static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
> >>>> +                          register_t *r, void *p)
> >>>> +{
> >>>> +    unsigned int reg;
> >>>> +    pci_sbdf_t sbdf;
> >>>> +    unsigned long data = ~0UL;
> >>>> +    unsigned int size = 1U << info->dabt.size;
> >>>> +
> >>>> +    sbdf.sbdf = MMCFG_BDF(info->gpa);
> >>>> +    reg = REGISTER_OFFSET(info->gpa);
> >>>> +
> >>>> +    if ( !vpci_mmio_access_allowed(reg, size) )
> >>>> +        return 0;
> >>>> +
> >>>> +    data = vpci_read(sbdf, reg, min(4u, size));
> >>>> +    if ( size == 8 )
> >>>> +        data |= (uint64_t)vpci_read(sbdf, reg + 4, 4) << 32;
> >>>> +
> >>>> +    *r = data;
> >>>> +
> >>>> +    return 1;
> >>>> +}
> >>>> +
> >>>> +static int vpci_mmio_write(struct vcpu *v, mmio_info_t *info,
> >>>> +                           register_t r, void *p)
> >>>> +{
> >>>> +    unsigned int reg;
> >>>> +    pci_sbdf_t sbdf;
> >>>> +    unsigned long data = r;
> >>>> +    unsigned int size = 1U << info->dabt.size;
> >>>> +
> >>>> +    sbdf.sbdf = MMCFG_BDF(info->gpa);
> >>>> +    reg = REGISTER_OFFSET(info->gpa);
> >>>> +
> >>>> +    if ( !vpci_mmio_access_allowed(reg, size) )
> >>>> +        return 0;
> >>>> +
> >>>> +    vpci_write(sbdf, reg, min(4u, size), data);
> >>>> +    if ( size == 8 )
> >>>> +        vpci_write(sbdf, reg + 4, 4, data >> 32);
> >>> I think those two helpers (and vpci_mmio_access_allowed) are very
> >>> similar to the existing x86 ones (see vpci_mmcfg_{read,write}), up to
> >>> the point where I would consider moving the shared code to vpci.c as
> >>> vpci_ecam_{read,write} and call them from the arch specific trap
> >>> handlers.
> >> Except that please can we stick to mcfg or mmcfg instead of ecam
> >> in names, as that's how the thing has been named in Xen from its
> >> introduction? I've just grep-ed the code base (case insensitively)
> >> and found no mention of ECAM. There are only a few "became".
> > I do understand that this is historically that we do not have ECAM in Xen,
> > but PCI is not about Xen. Thus, I think it is also acceptable to use
> > a commonly known ECAM for the code that works with ECAM.
> 
> ACPI, afaik, also doesn't call this ECAM. That's where MCFG / MMCFG
> actually come from, I believe.

My understanding is that "MCFG" is the name of the ACPI table that
describes the PCI config space [1]. The underlying PCI standard for the
memory mapped layout of the PCI config space is called ECAM. Here, it
makes sense to call it ECAM as it is firmware independent.

[1] https://wiki.osdev.org/PCI_Express