linux-kernel - Re: [PATCH] nvme: Add support for Apple 2018+ models

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Date:   Mon, 15 Jul 2019 18:43:25 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-nvme@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Paul Pawlowski <paul@...rm.io>
Subject: Re: [PATCH] nvme: Add support for Apple 2018+ models

On Mon, 2019-07-15 at 10:10 +0200, Christoph Hellwig wrote:
> > +	/*
> > +	 * Apple 2018 and latter variant has a few issues
> > +	 */
> > +	NVME_QUIRK_APPLE_2018			= (1 << 10),
> 
> We try to have quirks for the actual issue, so this should be one quirk
> for the irq vectors issues, and another for the sq entry size.  Note that
> NVMe actually has the concept of an I/O queue entry size (IOSQES in the
> Cc register based on values reported in the SQES field in Identify
> Controller.  Do these controllers report anything interesting there?

Ah good to know, I'll dig.

> At the very least I'd make all the terminology based on that and then
> just treat the Apple controllers as a buggy implementation of that model.

Yup, sounds good. I'll poke around tomorrow.

> Btw, are there open source darwin NVMe driver that could explain this
> mess a little better?

You wish...

> > @@ -504,8 +505,11 @@ static inline void nvme_write_sq_db(struct nvme_queue *nvmeq, bool write_sq)
> >  static void nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd,
> >  			    bool write_sq)
> >  {
> > +	u16 sq_actual_pos;
> > +
> >  	spin_lock(&nvmeq->sq_lock);
> > -	memcpy(&nvmeq->sq_cmds[nvmeq->sq_tail], cmd, sizeof(*cmd));
> > +	sq_actual_pos = nvmeq->sq_tail << nvmeq->sq_extra_shift;
> > +	memcpy(&nvmeq->sq_cmds[sq_actual_pos], cmd, sizeof(*cmd));
> 
> This is a little too magic.  I think we'd better off making sq_cmds
> a void array and use manual indexing, at least that makes it very
> obvious what is going on.

Ok. That's plan B as I described in the message. There's an advantage
to do that, it merges the indexing shift and the quirk shift into one.

I'll look into it & respin

> > -				nvmeq->sq_cmds, SQ_SIZE(nvmeq->q_depth));
> > +				nvmeq->sq_cmds, SQ_SIZE(nvmeq));
> 
> Btw, chaning SQ_SIZE to take the queue seems like something that should
> be split into a prep patch, making the main change a lot smaller.

Sure. Will do.

> > -	if (!polled)
> > +	if (!polled) {
> > +
> > +		/*
> > +		 * On Apple 2018 or later implementations, only vector 0 is accepted
> 
> Please fix the > 80 char line.

Ok.

Thanks for the review.

Cheers,
Ben.