Am 25.02.2020 um 16:53 schrieb Mark Brown:
On Tue, Feb 25, 2020 at 02:27:27PM +0100, Herbrechtsmeier Dr.-Ing. , Stefan wrote:
would it be acceptable to add an additional function to the struct
spi_controller which handle a transfer inside a NMI context or a panic? The
new function will transfer data via register polling without any lock.
That would need to happen as part of a wider change that made it
possible to use such an interface safely and did so, off the top of my
head it's not immediately obvious how one would do that. You'd need to
get the hardware into a sensible state and then do whatever needs doing
with some cooperation from the client driver in all this which is a bit
of an ask. It's not a trivial bit of work, but I do see the use case
and it's absolutely valid.
I see two possible solutions.
a) The complexity is handled inside the client. The client uses the
controller exclusive and isn’t allowed to use the new panic transfer
during a normal transfer.
b) The complexity is handled inside the controller. The controller is
shared between multiple slaves and a panic transfer must abort a running
transfer.
The first solution keeps the controller driver simple because only a new
polled transfer is needed. But the prepare and unprepare functions must
be lock free and power management must be handled lock free to be reused.
The second solution could lead to code duplication because an addition
panic prepare function must setup the controller from any state and must
abort a running transfer. Especially the abort could be complex and
difficult to test. Otherwise the new functionality could be used without
any constraints.
