Commit 4631f3ca authored by Niklas Schnelle's avatar Niklas Schnelle Committed by Heiko Carstens

s390/pci: clarify comment in s390_mmio_read/write

The existing comment was talking about reading in the write part
and vice versa. While we are here make it more clear why restricting
the syscalls to MIO capable devices is okay.
Signed-off-by: default avatarNiklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 41115582
...@@ -155,10 +155,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, ...@@ -155,10 +155,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
return -EINVAL; return -EINVAL;
/* /*
* Only support read access to MIO capable devices on a MIO enabled * We only support write access to MIO capable devices if we are on
* system. Otherwise we would have to check for every address if it is * a MIO enabled system. Otherwise we would have to check for every
* a special ZPCI_ADDR and we would have to do a get_pfn() which we * address if it is a special ZPCI_ADDR and would have to do
* don't need for MIO capable devices. * a get_pfn() which we don't need for MIO capable devices. Currently
* ISM devices are the only devices without MIO support and there is no
* known need for accessing these from userspace.
*/ */
if (static_branch_likely(&have_mio)) { if (static_branch_likely(&have_mio)) {
ret = __memcpy_toio_inuser((void __iomem *) mmio_addr, ret = __memcpy_toio_inuser((void __iomem *) mmio_addr,
...@@ -282,10 +284,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr, ...@@ -282,10 +284,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr,
return -EINVAL; return -EINVAL;
/* /*
* Only support write access to MIO capable devices on a MIO enabled * We only support read access to MIO capable devices if we are on
* system. Otherwise we would have to check for every address if it is * a MIO enabled system. Otherwise we would have to check for every
* a special ZPCI_ADDR and we would have to do a get_pfn() which we * address if it is a special ZPCI_ADDR and would have to do
* don't need for MIO capable devices. * a get_pfn() which we don't need for MIO capable devices. Currently
* ISM devices are the only devices without MIO support and there is no
* known need for accessing these from userspace.
*/ */
if (static_branch_likely(&have_mio)) { if (static_branch_likely(&have_mio)) {
ret = __memcpy_fromio_inuser( ret = __memcpy_fromio_inuser(
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment