netdev - RE: [Intel-wired-lan] [RFC PATCH] i40e: enable PCIe relax ordering for SPARC

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Date:   Thu, 8 Dec 2016 10:31:21 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexander Duyck' <alexander.duyck@...il.com>,
        Tushar Dave <tushar.n.dave@...cle.com>
CC:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Netdev <netdev@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [RFC PATCH] i40e: enable PCIe relax ordering
 for SPARC

From: Alexander Duyck
> Sent: 05 December 2016 21:55
...
> > @@ -1010,6 +1018,11 @@ int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring)
> >          */
> >         tx_ring->size += sizeof(u32);
> >         tx_ring->size = ALIGN(tx_ring->size, 4096);
> > +#ifdef CONFIG_SPARC
> > +       tx_ring->dma_attrs = DMA_ATTR_WEAK_ORDERING;
> > +#else
> > +       tx_ring->dma_attrs = 0;
> > +#endif
> >         tx_ring->desc = dma_alloc_coherent(dev, tx_ring->size,
> >                                            &tx_ring->dma, GFP_KERNEL);
> >         if (!tx_ring->desc) {
> 
> Also not a fan of adding yet ring attribute.  Is there any reason why
> you couldn't simply add a set of inline functions at the start of
> i40e_txrx.c that could replace the DMA map/unmap operations in this
> code but pass either 0 or DMA_ATTR_WEAK_ORDERING as needed for the
> drivers?  Then the x86 code doesn't have to change while the SPARC
> code will be able to be passed the attribute.

Or use something like:
#ifdef CONFIG_SPARC
       #define RING_DMA_ATTR DMA_ATTR_WEAK_ORDERING
#else
       #define RING_DMA_ATTR 0
#endif
and pass the constant to the function calls.

Is there actually ever a problem passing DMA_ATTR_WEAK_ORDERING?
I'd guess that it will be ignored if it can't be implemented (or isn't needed).

	David