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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 9 Apr 2020 12:41:13 +0200
Message-ID: <CAK8P3a1RXUXs5oYjB=Jq5cpvG11eTnmJ+vc18_-0fzgTH6envA@mail.gmail.com>
Subject: Re: [PATCH V9 9/9] virtio: Intel IFC VF driver for VDPA
To:     Jason Wang <jasowang@redhat.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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On Thu, Mar 26, 2020 at 3:08 PM Jason Wang <jasowang@redhat.com> wrote:
>
> From: Zhu Lingshan <lingshan.zhu@intel.com>
>
> This commit introduced two layers to drive IFC VF:
>
> (1) ifcvf_base layer, which handles IFC VF NIC hardware operations and
>     configurations.
>
> (2) ifcvf_main layer, which complies to VDPA bus framework,
>     implemented device operations for VDPA bus, handles device probe,
>     bus attaching, vring operations, etc.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> Signed-off-by: Bie Tiwei <tiwei.bie@intel.com>
> Signed-off-by: Wang Xiao <xiao.w.wang@intel.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

> +
> +#define IFCVF_QUEUE_ALIGNMENT  PAGE_SIZE
> +#define IFCVF_QUEUE_MAX                32768
> +static u16 ifcvf_vdpa_get_vq_align(struct vdpa_device *vdpa_dev)
> +{
> +       return IFCVF_QUEUE_ALIGNMENT;
> +}

This fails to build on arm64 with 64kb page size (found in linux-next):

/drivers/vdpa/ifcvf/ifcvf_main.c: In function 'ifcvf_vdpa_get_vq_align':
arch/arm64/include/asm/page-def.h:17:20: error: conversion from 'long
unsigned int' to 'u16' {aka 'short unsigned int'} changes value from
'65536' to '0' [-Werror=overflow]
   17 | #define PAGE_SIZE  (_AC(1, UL) << PAGE_SHIFT)
      |                    ^
drivers/vdpa/ifcvf/ifcvf_base.h:37:31: note: in expansion of macro 'PAGE_SIZE'
   37 | #define IFCVF_QUEUE_ALIGNMENT PAGE_SIZE
      |                               ^~~~~~~~~
drivers/vdpa/ifcvf/ifcvf_main.c:231:9: note: in expansion of macro
'IFCVF_QUEUE_ALIGNMENT'
  231 |  return IFCVF_QUEUE_ALIGNMENT;
      |         ^~~~~~~~~~~~~~~~~~~~~

It's probably good enough to just not allow the driver to be built in that
configuration as it's fairly rare but unfortunately there is no simple Kconfig
symbol for it.

In a similar driver, we did

config VMXNET3
        tristate "VMware VMXNET3 ethernet driver"
        depends on PCI && INET
        depends on !(PAGE_SIZE_64KB || ARM64_64K_PAGES || \
                     IA64_PAGE_SIZE_64KB || MICROBLAZE_64K_PAGES || \
                     PARISC_PAGE_SIZE_64KB || PPC_64K_PAGES)

I think we should probably make PAGE_SIZE_64KB a global symbol
in arch/Kconfig and have it selected by the other symbols so drivers
like yours can add a dependency for it.

         Arnd