netdev - Re: [PATCH mlx5-next 4/4] net/mlx5: Remove spinlock support from mlx5

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Date:   Fri, 25 Jan 2019 18:16:31 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     Jason Gunthorpe <jgg@...lanox.com>,
        "saeedm@....mellanox.co.il" <saeedm@....mellanox.co.il>
CC:     Eran Ben Elisha <eranbe@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH mlx5-next 4/4] net/mlx5: Remove spinlock support from
 mlx5_write64

On Mon, 2019-01-21 at 18:22 +0000, Jason Gunthorpe wrote:
> On Mon, Jan 21, 2019 at 10:12:58AM -0800, Saeed Mahameed wrote:
> > On Mon, Jan 21, 2019 at 8:46 AM Jason Gunthorpe <jgg@...lanox.com>
> > wrote:
> > > On Sat, Jan 19, 2019 at 12:43:14AM -0700, Leon Romanovsky wrote:
> > > > You need to do one of two things:
> > > > 1. Require CONFIG_64BIT and delete this 32bit code.
> > > > 2. Declare global mlx5 DB spinlock and use on 32bit systems,
> > > > something
> > > > like this:
> > > > #if BITS_PER_LONG == 64
> > > >  __raw_writeq(*(u64 *)val, dest);
> > > > #else
> > > >   spin_lock_irqsave(doorbell_lock, flags);
> > > >   __raw_writel((__force u32) val[0], dest);
> > > >   __raw_writel((__force u32) val[1], dest + 4);
> > > >    spin_unlock_irqrestore(doorbell_lock, flags);
> > > > #endif
> > > 
> > > And why is this code using the __raw_ versions? Seems wrong
> > > too...
> > > 
> > 
> > for 64 and 32 as well?
> 
> yes
> 
> > what is wrong with the raw version ?
> 
> It should only be used by arch code (or in drivers linked to a
> specific arch). The actual properties of the 'raw' version are arch
> specific and make it hard to know if the driver will work on
> different
> archs. ie some arches may not byte swap their raw accessors, or may
> omit barriers.
> 
> Most likely this just wants to be writeq for 64 bit and
> writel_relaxed() & writel() for 32 bit - unless there was some reason
> to have used __raw versions in the first place (in which case a
> comment is missing).

Ok, after some internal discussion it seems that
{read,write}{b,w,l,q}_relaxed() can be used instead of the __raw API
currently used in the driver, Adding as a future task.

This has nothing to do the the current cleanup patch.

Thanks,
Saeed.

> 
> Jason