[Nouveau] PR: nv50 IB-mode DMA crash fixes

[Ilia Mirkin]

On Sun, Dec 3, 2023 at 11:37 AM Monty Montgomery <xiphmont at gmail.com> wrote:
> 1) The nv50 DMA code clearly believed push buffers could not (or
> should not) exceed NV50_DMA_PUSH_MAX_LENGTH, when my analysis logging
> shows that they regularly exceed this maximum by an order of magnitude
> or more.  Was the assumption originally true?  If so, when/why did it
> change?  Is the more correct fix to enforce individual pushbuf size
> limits?

The BO itself can be artibrarily sized. However the length stored in
the ring only has so many bits, so that provides a natural maximum.

https://envytools.readthedocs.io/en/latest/hw/fifo/dma-pusher.html#ib-mode

This might be different on newer gens though.

Cheers,

  -ilia