linux-kernel - RE: [PATCH 3/8] thunderbolt: Use 32-bit writes when writing ring producer/consumer

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Message-ID: <0f3a47d8133945b181d623ea6e0d53f2@AcuMS.aculab.com>
Date:   Fri, 5 Jul 2019 16:04:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Yehezkel Bernat' <yehezkelshb@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Lukas Wunner <lukas@...ner.de>,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        "Anthony Wong" <anthony.wong@...onical.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: [PATCH 3/8] thunderbolt: Use 32-bit writes when writing ring
 producer/consumer

From: Yehezkel Bernat
> Sent: 05 July 2019 12:10
> On Fri, Jul 5, 2019 at 12:58 PM Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> >
> > The register access should be using 32-bit reads/writes according to the
> > datasheet. With the previous generation hardware 16-bit writes have been
> > working but starting with ICL this is not the case anymore so fix
> > producer/consumer register update to use correct width register address.
> >
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> >  drivers/thunderbolt/nhi.c | 26 ++++++++++++++++++++++----
> >  1 file changed, 22 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/thunderbolt/nhi.c b/drivers/thunderbolt/nhi.c
> > index 27fbe62c7ddd..09242653da67 100644
> > --- a/drivers/thunderbolt/nhi.c
> > +++ b/drivers/thunderbolt/nhi.c
> > @@ -143,9 +143,24 @@ static void __iomem *ring_options_base(struct tb_ring *ring)
> >         return io;
> >  }
> >
> > -static void ring_iowrite16desc(struct tb_ring *ring, u32 value, u32 offset)
> > +static void ring_iowrite_prod(struct tb_ring *ring, u16 prod)
> >  {
> > -       iowrite16(value, ring_desc_base(ring) + offset);
> > +       u32 val;
> > +
> > +       val = ioread32(ring_desc_base(ring) + 8);
> > +       val &= 0x0000ffff;
> > +       val |= prod << 16;
> > +       iowrite32(val, ring_desc_base(ring) + 8);
> > +}
> > +
> > +static void ring_iowrite_cons(struct tb_ring *ring, u16 cons)
> > +{
> > +       u32 val;
> > +
> > +       val = ioread32(ring_desc_base(ring) + 8);
> > +       val &= 0xffff0000;
> > +       val |= cons;
> > +       iowrite32(val, ring_desc_base(ring) + 8);
> >  }
> >
> >  static void ring_iowrite32desc(struct tb_ring *ring, u32 value, u32 offset)
> > @@ -197,7 +212,10 @@ static void ring_write_descriptors(struct tb_ring *ring)
> >                         descriptor->sof = frame->sof;
> >                 }
> >                 ring->head = (ring->head + 1) % ring->size;
> > -               ring_iowrite16desc(ring, ring->head, ring->is_tx ? 10 : 8);
> > +               if (ring->is_tx)
> > +                       ring_iowrite_prod(ring, ring->head);
> > +               else
> > +                       ring_iowrite_cons(ring, ring->head);
> 
> Really a matter of taste, but maybe you want to consider having a single
> function, with a 3rd parameter, bool is_tx.
> The calls here will be unified to:
>         ring_iowrite(ring, ring->head, ring->is_tx);
> (No condition is needed here).
> 
> The implementation uses the new parameter to decide which part of the register
> to mask, reducing the code duplication (in my eyes):
> 
>         val = ioread32(ring_desc_base(ring) + 8);
>         if (is_tx) {
>                 val &= 0x0000ffff;
>                 val |= value << 16;
>         } else {
>                 val &= 0xffff0000;
>                 val |= value;
>         }
>         iowrite32(val, ring_desc_base(ring) + 8);
> 
> I'm not sure if it improves the readability or makes it worse. Your call.

Gah, that is all horrid beyond belief.
If a 32bit write is valid then the hardware must not be updating
the other 16 bits.
In which case the driver knows what they should be.
So it can do a single 32bit write of the required value.

	David

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