netdev - Re: [RDMA RFC v6 00/16] Intel RDMA Driver Updates 2020-05-19

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Message-ID: <20200601142840.GE4962@mellanox.com>
Date:   Mon, 1 Jun 2020 11:28:40 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     "Saleem, Shiraz" <shiraz.saleem@...el.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        "poswald@...e.com" <poswald@...e.com>
Subject: Re: [RDMA RFC v6 00/16] Intel RDMA Driver Updates 2020-05-19

On Fri, May 29, 2020 at 03:21:05PM +0000, Saleem, Shiraz wrote:
> > Subject: Re: [RDMA RFC v6 00/16] Intel RDMA Driver Updates 2020-05-19
> > 
> 
> [......]
> 
> > 
> > I'm looking on it and see static assignments, to by dynamic you will need "to play"
> > with hw_shifts/hw_masks later, but you don't. What am I missing?
> > 
> > +	for (i = 0; i < IRDMA_MAX_SHIFTS; ++i)
> > +		dev->hw_shifts[i] = i40iw_shifts[i];
> > +
> > +	for (i = 0; i < IRDMA_MAX_MASKS; ++i)
> > +		dev->hw_masks[i] = i40iw_masks[i];
> > 
> > >
> > > we still need to use the custom macro FLD_LS_64 without FIELD_PREP in
> > > this case as FIELD_PREP expects compile time constants.
> > > +#define FLD_LS_64(dev, val, field)	\
> > > +	(((u64)(val) << (dev)->hw_shifts[field ## _S]) &
> > > +(dev)->hw_masks[field ## _M])
> > > And the shifts are still required for these fields which causes a bit
> > > of inconsistency
> > >
> 
> 
> The device hw_masks/hw_shifts array store masks/shifts of those
> descriptor fields that have same name across HW generations but
> differ in some attribute such as field width. Yes they are statically assigned,
> initialized with values from i40iw_masks and icrdma_masks, depending on
> the HW generation. We can even use GENMASK for the values in
> i40iw_masks[] , icrdma_masks[] but FIELD_PREP cant be used on
> dev->hw_masks[]

So compute the shift and mask when building i40iw_shifts array using
the compile time constant?

Jason