Re: [PATCH] pci/switchtec: Don't use completion's wait queue

[Logan Gunthorpe <logang@deltatee.com>]

On 04/10/17 03:50 AM, Sebastian Andrzej Siewior wrote:
> The poll callback is using completion's wait_queue_head_t member and
> puts it in poll_wait() so the poll() caller gets a wakeup after command
> completed. This does not work on RT because we don't have a
> wait_queue_head_t in our completion implementation. Nobody in tree does
> like that in tree so this is the only driver that breaks.

I'm sorry but this seems a bit crazy to me. Driver's can't poll on 
completions because an out of tree implementation changes them in a 
weird way??! Just because no one in-tree does it now doesn't make it 
invalid.

But at the very least, if we _absolutely_ have to patch this out, you 
shouldn't make it so convoluted. Just replace the struct completion with 
a wait queue and a done flag (which is what a completion is). Don't move 
the wait queue into switchtec_dev and don't use an unnecessary counter. 
And certainly don't think about merging it with another wait queue that 
has completely different wake events and waiters.

In any case, I haven't tested the patch, but I'm pretty sure it's not 
correct. There can be multiple switchtec_user's queued up and this patch 
will essentially complete them all once any one of them finishes and 
cmd_cnt increments.

So this patch gets a NAK from me.

Logan