DMA reordering possible ?

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Hi all,

Following questions can be of naïve nature. Kindly, help me to clarify
the points.
Thanks in Advance.

1) Consider a situation where a PCIe device has requested a DMA Write
operation followed by an MSI based interrupt. Upon receiving the
interrupt, the software will read/check the DMAed data. Now, even if
the device is guaranteeing the ordering between the two (issuing one
after the other), whether the I/O controller OR chipset can
reorder/buffer them? This may result into getting interrupt before the
data is DMAed resulting into software reading invalid data. Here data
is residing into internal buffers of I/O controller and CPU is trying
to read from memory. Whether such DMA reordering can happen/is allowed
at all? Whether I/O controller can employ such intelligence(any kind
of DMA reordering) for gaining some performance advantage? Mainly,
focus is on high-end server class platforms having 8 or 16 cores with
many peripherals.

2) If above situation is at all possible, then to avoid such situation
is the responsibility of the device or the driver for that device?
Mainly, both the components (device and driver) expected to be generic
in nature (platform, I/O controller independent).

3) In continuation, if driver has to handle such situations, then how
to handle such cases in Linux device driver? Any API is there for
pending DMA flush/sync in I/O controller? I am aware of rmb(), wmb() &
mb() which ensures ordering from CPU side i.e. slave read/writes.
Anythings similar for DMA operations ?

Kindly, update me if i am missing something.

Any info,link or reference will be of great help.

Thanks and Regards,
Yogeshwar
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