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Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller

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On Thursday 03 March 2016 13:36:49 Russell King - ARM Linux wrote:
> On Thu, Mar 03, 2016 at 02:08:19PM +0100, Arnd Bergmann wrote:
> > On Thursday 03 March 2016 13:01:13 Marc Zyngier wrote:
> > > > +/* Routines to acknowledge, disable and enable interrupts */
> > > > +static void rps_mask_irq(struct irq_data *d)
> > > > +{
> > > > +     u32 mask = BIT(d->hwirq);
> > > > +
> > > > +     iowrite32(mask, rps_data.base + RPS_MASK);
> > > 
> > > I do question the use of iowrite32 here (and its ioread32 pendent
> > > anywhere else), as it actually translates in a writel, which contains a
> > > memory barrier. Do you have any case that requires the use of such a
> > > barrier? if not, consider switching to relaxed accessors (which are the
> > > 
> > 
> > I really ask everyone to do the opposite: we have seen several drivers
> > blindlessly using the relaxed accessors and actually introducing bugs
> > that way, so I'd rather see the readl/writel ones used by default.
> 
> I actually agree with Marc - we have far too many drivers using the
> barriered IO accessors, which are really very expensive on 32-bit
> ARM.
> 
> For most ARM systems, the rules are quite simple: a write which causes
> DMA memory to be accessed by the device must be using the barriered
> IO accessor, and a read from a DMA status register must be too.
> Everything else need not be.  Barriered IO accessors are only about
> access ordering.

My main worry is really about code getting copied from drivers that
are fine with just relaxed accessors into other drivers by developers
that have never heard about the difference and just want to follow
best practices.

	Arnd

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[PATCH 00/17] Add Initial support for PLX Technology OX810SE Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
  [PATCH 06/17] reset: Add PLX Technology Reset Controller driver Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
    Re: [PATCH 06/17] reset: Add PLX Technology Reset Controller driver Philipp Zabel <p.zabel@pengutronix.de> - 2016-03-03 15:20 +0100
      Re: [PATCH 06/17] reset: Add PLX Technology Reset Controller driver Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 15:40 +0100
        Re: [PATCH 06/17] reset: Add PLX Technology Reset Controller driver Philipp Zabel <p.zabel@pengutronix.de> - 2016-03-03 16:10 +0100
  [PATCH 07/17] dt-bindings: Add PLX Technology Reset Controller bindings Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
    Re: [PATCH 07/17] dt-bindings: Add PLX Technology Reset Controller  bindings Philipp Zabel <p.zabel@pengutronix.de> - 2016-03-03 15:30 +0100
      Re: [PATCH 07/17] dt-bindings: Add PLX Technology Reset Controller  bindings Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 15:30 +0100
        Re: [PATCH 07/17] dt-bindings: Add PLX Technology Reset Controller  bindings Philipp Zabel <p.zabel@pengutronix.de> - 2016-03-03 15:40 +0100
  [PATCH 05/17] dt-bindings: Add PLX Technology RPS Timer bindings Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
  [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
    Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Arnd Bergmann <arnd@arndb.de> - 2016-03-03 14:10 +0100
      Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-03-03 14:40 +0100
        Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Arnd Bergmann <arnd@arndb.de> - 2016-03-03 18:40 +0100
    Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Marc Zyngier <marc.zyngier@arm.com> - 2016-03-03 14:10 +0100
    RE: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller "Ma Haijun" <mahaijuns@gmail.com> - 2016-03-03 16:40 +0100
      Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 18:00 +0100
        Re: [PATCH 02/17] irqchip: Add PLX Technology RPS IRQ Controller Marc Zyngier <marc.zyngier@arm.com> - 2016-03-03 18:20 +0100
  [PATCH 09/17] dt-bindings: Add PLX Technology OXNAS Standard Clocks bindings Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:00 +0100
  Re: [PATCH 00/17] Add Initial support for PLX Technology OX810SE Arnd Bergmann <arnd@arndb.de> - 2016-03-03 13:30 +0100
    Re: [PATCH 00/17] Add Initial support for PLX Technology OX810SE Neil Armstrong <narmstrong@baylibre.com> - 2016-03-03 13:40 +0100

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