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

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

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.

	--yliu