netdev - Re: [RFC 1/2] vhost: IFC VF hardware operation layer

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Date:   Mon, 21 Oct 2019 18:31:40 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>
Cc:     mst@...hat.com, jasowang@...hat.com, alex.williamson@...hat.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, dan.daly@...el.com,
        cunming.liang@...el.com, tiwei.bie@...el.com, jason.zeng@...el.com,
        zhiyuan.lv@...el.com
Subject: Re: [RFC 1/2] vhost: IFC VF hardware operation layer

On Mon, Oct 21, 2019 at 05:55:33PM +0800, Zhu, Lingshan wrote:
> 
> On 10/16/2019 5:53 PM, Simon Horman wrote:
> > Hi Zhu,
> > 
> > thanks for your patch.
> > 
> > On Wed, Oct 16, 2019 at 09:10:40AM +0800, Zhu Lingshan wrote:

...

> > > +static void ifcvf_read_dev_config(struct ifcvf_hw *hw, u64 offset,
> > > +		       void *dst, int length)
> > > +{
> > > +	int i;
> > > +	u8 *p;
> > > +	u8 old_gen, new_gen;
> > > +
> > > +	do {
> > > +		old_gen = ioread8(&hw->common_cfg->config_generation);
> > > +
> > > +		p = dst;
> > > +		for (i = 0; i < length; i++)
> > > +			*p++ = ioread8((u8 *)hw->dev_cfg + offset + i);
> > > +
> > > +		new_gen = ioread8(&hw->common_cfg->config_generation);
> > > +	} while (old_gen != new_gen);
> > Would it be wise to limit the number of iterations of the loop above?
> Thanks but I don't quite get it. This is used to make sure the function
> would get the latest config.

I am worried about the possibility that it will loop forever.
Could that happen?

...

> > > +static void io_write64_twopart(u64 val, u32 *lo, u32 *hi)
> > > +{
> > > +	iowrite32(val & ((1ULL << 32) - 1), lo);
> > > +	iowrite32(val >> 32, hi);
> > > +}
> > I see this macro is also in virtio_pci_modern.c
> > 
> > Assuming lo and hi aren't guaranteed to be sequential
> > and thus iowrite64_hi_lo() cannot be used perhaps
> > it would be good to add a common helper somewhere.
> Thanks, I will try after this IFC patchwork, I will cc you.

Thanks.

...