Re: [PATCH] nvme: Fix nvme_get/set_features() with a NULL result pointer

[Jens Axboe]

On 08/25/2016 01:54 AM, Andy Lutomirski wrote:
> On Thu, Aug 25, 2016 at 12:38 AM, Christoph Hellwig <hch@xxxxxx> wrote:
> > Ooops, yes.
> >
> > Are you looking into new nvme_set_features users?  Another thing
> > we need to tackle is either replacing dma_addr argument with a
> > a real kernel pointer (or just kill it until users show up)
>
> I am, and I have a patch to do the former (and to add a length
> argument).  But that's not -stable material.
>
> While I have your attention: the new use is to enable APST (power
> saving).  In theory, it seems like I should integrate with dev_pm_qos
> so that the standard interface for setting a latency limit will work,
> but, on brief inspection, there are literally no drivers in the entire
> tree that do this.  Am I missing something?  My current draft patch
> just adds a sysfs attribute.  (It saves a *lot* of power on my laptop,
> so supporting APST is worth doing.)

Care to send out what you have? I'd be interested in seeing how much I
can save on my laptop, haven't played with APST yet.

--
Jens Axboe