Kconfig: no userspace I/O on s390.
Subsystems (2)
PATCH 6/8 Kconfig: no userspace I/O on s390.
From: Martin Schwidefsky <[email protected]>
Hide the config menu for userspace I/O on s390.
Goes on top of gregkh-driver-uio.patch.
---
drivers/uio/Kconfig | 2 ++ 1 files changed, 2 insertions(+)
drivers/uio/Kconfig +2 -0
@@ -1,4 +1,6 @@ menu "Userspace I/O" + depends on !S390 + config UIO tristate "Userspace I/O drivers" default n
Quoted 3 lines · Martin Schwidefsky
From: Martin Schwidefsky <[email protected]>
Hide the config menu for userspace I/O on s390.
Why? Who says s390 can't have userspace I/O drivers someday?
thanks,
greg k-h
Quoted 3 lines · Greg KH
Quoted 1 line
Hide the config menu for userspace I/O on s390.
Why? Who says s390 can't have userspace I/O drivers someday?
Theoretically yes, but in practice this is very unlikely to happen. Some reasons why:
1) There are only very few device drivers for s390, the few we need we'll do as kernel space drivers
2) The irq abstraction of uio is awkward. The irq handler uses a 32-bit integer. On s390 each ccw device has it's own irq and ccw devices are identified with a string "x.y.zzzz". Then there are devices that deliver external interrupts where a 16-bit number is used to identify the source. You could invent some mapping logic of a 32 bit integer to all the possible interrupt sources but it doesn't really match.
3) s390 doesn't use memory mapped i/o, you always need to execute a privileged instruction to trigger activity on the device, e.g. ssch for a ccw device, siga for qdio, nqap for crypto, ...
So I have my doubts that we will ever see a uio driver for s390. If we do we can unhide the config menu again.
Signature · 4 lines
blue skies, Martin. "Reality continues to ruin my life." - Calvin.
Quoted 19 lines · Martin Schwidefsky
Quoted 3 lines · Greg KH
Quoted 1 line
Hide the config menu for userspace I/O on s390.
Why? Who says s390 can't have userspace I/O drivers someday?
Theoretically yes, but in practice this is very unlikely to happen. Some reasons why:
1) There are only very few device drivers for s390, the few we need we'll do as kernel space drivers
2) The irq abstraction of uio is awkward. The irq handler uses a 32-bit integer. On s390 each ccw device has it's own irq and ccw devices are identified with a string "x.y.zzzz". Then there are devices that deliver external interrupts where a 16-bit number is used to identify the source. You could invent some mapping logic of a 32 bit integer to all the possible interrupt sources but it doesn't really match.
3) s390 doesn't use memory mapped i/o, you always need to execute a privileged instruction to trigger activity on the device, e.g. ssch for a ccw device, siga for qdio, nqap for crypto, ...
Quoted 2 lines
So I have my doubts that we will ever see a uio driver for s390. If we do we can unhide the config menu again.
Ok, that's find, can you bounce me the patch that made this change again?
thanks,
greg k-h