Re: [dpdk-dev] [ [PATCH v2] 05/13] virtio: change io_base datatype from uint32_t to uint64_type

[Santosh Shukla <sshukla@mvista.com>]

On Thu, Dec 17, 2015 at 12:49 PM, Yuanhan Liu
<yuanhan.liu@linux.intel.com> wrote:
> On Wed, Dec 16, 2015 at 08:35:58PM +0530, Santosh Shukla wrote:
>> On Wed, Dec 16, 2015 at 8:28 PM, Yuanhan Liu
>> <yuanhan.liu@linux.intel.com> wrote:
>> > On Wed, Dec 16, 2015 at 08:09:40PM +0530, Santosh Shukla wrote:
>> >> On Wed, Dec 16, 2015 at 7:53 PM, Yuanhan Liu
>> >> <yuanhan.liu@linux.intel.com> wrote:
>> >> > On Wed, Dec 16, 2015 at 07:31:57PM +0530, Santosh Shukla wrote:
>> >> >> On Wed, Dec 16, 2015 at 7:18 PM, Yuanhan Liu
>> >> >> <yuanhan.liu@linux.intel.com> wrote:
>> >> >> > On Mon, Dec 14, 2015 at 06:30:24PM +0530, Santosh Shukla wrote:
>> >> >> >> In x86 case io_base to store ioport address not more than 65535 ioports. i.e..0
>> >> >> >> to ffff but in non-x86 case in particular arm64 it need to store more than 32
>> >> >> >> bit address so changing io_base datatype from 32 to 64.
>> >> >> >>
>> >> >> >> Signed-off-by: Santosh Shukla <sshukla@mvista.com>
>> >> >> >> ---
>> >> >> >>  drivers/net/virtio/virtio_ethdev.c |    2 +-
>> >> >> >>  drivers/net/virtio/virtio_pci.h    |    4 ++--
>> >> >> >>  2 files changed, 3 insertions(+), 3 deletions(-)
>> >> >> >>
>> >> >> >> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
>> >> >> >> index d928339..620e0d4 100644
>> >> >> >> --- a/drivers/net/virtio/virtio_ethdev.c
>> >> >> >> +++ b/drivers/net/virtio/virtio_ethdev.c
>> >> >> >> @@ -1291,7 +1291,7 @@ eth_virtio_dev_init(struct rte_eth_dev *eth_dev)
>> >> >> >>               return -1;
>> >> >> >>
>> >> >> >>       hw->use_msix = virtio_has_msix(&pci_dev->addr);
>> >> >> >> -     hw->io_base = (uint32_t)(uintptr_t)pci_dev->mem_resource[0].addr;
>> >> >> >> +     hw->io_base = (uint64_t)(uintptr_t)pci_dev->mem_resource[0].addr;
>> >> >> >
>> >> >> > I'd suggest to move the io_base assignment (and cast) into virtio_ioport_init()
>> >> >> > so that we could do the correct cast there, say cast it to uint32_t for
>> >> >> > X86, and uint64_t for others.
>> >> >> >
>> >> >>
>> >> >> Ok.
>> >> >>
>> >> >> This was deliberately done considering your 1.0 virtio spec patch do
>> >> >> care for uint64_t types and in arm64 case, If I plan to use those
>> >> >> future patches, IMO it make more sense to me keep it in uint64_t way;
>> >> >
>> >> > I did different cast, 32 bit for legacy virtio pci device, and 64 bit
>> >> > for modern virtio pci device.
>> >> >
>> >> >> Also in x86 case max address could of type 0x1000-101f and so forth;
>> >> >> changing data-type to uint64_t default wont effect such address,
>> >> >> right?
>> >> >
>> >> > Right, but what's the harm of doing the right cast? :)
>> >> >
>> >>
>> >> Agree.
>> >>
>> >> >> And hw->io_base by looking at virtio_pci.h function like
>> >> >> inb/outb etc.. takes io_base address as unsigned long types which is
>> >> >> arch dependent; i.e.. 4 byte for 32 bit and 8 for 64 bit so the lower
>> >> >> level rd/wr apis are taking care of data-types accordingly.
>> >> >
>> >> > Didn't get it. inb/outb takes "unsigned short" arguments, but not
>> >> > "unsigned long".
>> >> >
>> >>
>> >> sys/io.h in x86 case using unsigned short int  types..
>> >>
>> >> include/asm-generic/io.h for arm64 using it unsigned long (from linux
>> >> header files)
>> >>
>> >> In such case keeping
>> >> #define VIRTIO_PCI_REG_ADDR(hw, reg) \
>> >> (unsigned short)((hw)->io_base + (reg))
>> >>
>> >> would be x86 specific and what I thought and used in this patch is
>> >>
>> >> #define VIRTIO_PCI_REG_ADDR(hw, reg) \
>> >> (unsigned long)((hw)->io_base + (reg))
>> >>
>> >> to avoid ifdef ARM or non-x86..clutter, I know data-type is not right
>> >> fit for x86 sys/io.h but considering possible address inside
>> >> hw->io_base, wont effect functionality and performance my any mean.
>> >> That is why at virtio_ethdev_init() i choose to keep it in hw->io_base
>> >> = (uint64_t) types.
>> >>
>> >> Otherwise I'll have to duplicate VIRTIO_PCI_REG_XXX definition for
>> >> non-x86 case, Pl. suggest better alternative. Thanks
>> >
>> >
>> > My understanding is that if you have done the right cast in the first
>> > time (at the io_base assignment), casting from a short type to a longer
>> > type will not matter: the upper bits will be filled with zero.
>> >
>> > So, I guess we are fine here. I'm thinking that the extra cast in
>> > VIRTIO_PCI_REG_ADDR() is not necessary, as C will do the right
>> > cast for different inb(), say cast it to "unsigned short" for x86,
>> > and "unsigned long" for your arm implementation. The same to
>> > other io helpers.
>> >
>>
>> so to summarize and correct me if i misunderstood,
>> keep hw->io_base = (uint64_t)
>
> I still want a different explicit cast for x86 and non-x86. And
> actually, we should cast it to (unsigned short) but not (uint32_t)
> for x86, don't we?
>
> On the other hand, we may cast it to uint64_t unconditionally,
> and then have an explicit sanity check for io_base for x86, say
>
>         if ((unsigned short)hw->io_base != hw->io_base) {
>                 PMD_INIT_LOG(ERR, "invalid io port: %"PRIx64, ...);
>                 return -1;
>         }
>
> It's better than the (unsigned short) cast, as the later simply hides
> issue when something went wrong, though it's not rare.
>
> What do you think of that?
>

Liked the later part which is casting uint64_t unconditionally and
keeping a (unsigned short) check for x86 case. We'll do it in v3.

>> and remove extra cast {i.e.. (unsigned short) for x86 or (unsigned
>> long) for non-x86/arm64 case} in   VIRTIO_PCI_REG_ADDR().
>
> Technically speaking, yes, we don't need this kind of cast.
>

Ok.

>         --yliu