linux-kernel - Re: [PATCH] nvme/pci: Use host managed power state for suspend

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Message-ID: <20190513134708.GB15318@localhost.localdomain>
Date:   Mon, 13 May 2019 07:47:08 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
Cc:     "Busch, Keith" <keith.busch@...el.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        linux-pm <linux-pm@...r.kernel.org>,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Kai Heng Feng <kai.heng.feng@...onical.com>,
        Rafael Wysocki <rafael@...nel.org>
Subject: Re: [PATCH] nvme/pci: Use host managed power state for suspend

On Sat, May 11, 2019 at 11:06:35PM -0700, Chaitanya Kulkarni wrote:
> On 5/10/19 2:35 PM, Keith Busch wrote:
> >   
> > +int nvme_set_power(struct nvme_ctrl *ctrl, unsigned ps)

> dev->ctrl.npss is u8 can we use same data type here ?
> If this is due to last_ps we use as a result and then call set_power may 
> be we can change the type of last_ps ?
> OR
> can we please use unsigned int to avoid possible warnings ?

Right, the feature uses a 32-bit value even though only the first byte
is defined at the moment. It's just for foward compatibility. Will make
this a u32.

> > +int nvme_get_power(struct nvme_ctrl *ctrl, u32 *result)
> > +{
> > +	struct nvme_command c;
> May be use struct nvme_command c {} so we can get rid of the memset() call.

Good point.

> > +	union nvme_result res;
> > +	int ret;
> > +
> > +	if (!result)
> > +		return -EINVAL;
> > +
> > +	memset(&c, 0, sizeof(c));
> > +	c.features.opcode = nvme_admin_get_features;
> > +	c.features.fid = cpu_to_le32(NVME_FEAT_POWER_MGMT);
> > +
> > +	ret = __nvme_submit_sync_cmd(ctrl->admin_q, &c, &res,
> > +			NULL, 0, 0, NVME_QID_ANY, 0, 0, false);
> > +	if (ret >= 0)
> > +		*result = le32_to_cpu(res.u32);
>
> May be add a check for result here in above if before deref pointer :-
> 	if (ret >= 0 && result)

I have it checked at the top of the function since it doesn't make much
sense to call this without a way to return the result.