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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan