linux-kernel - Re: [PATCH] irqchip/gic-v3: Fix IPRIORITYR can't perform byte operations in GIC-600

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Message-ID: <20210330130637.GA26263@lpieralisi>
Date:   Tue, 30 Mar 2021 14:06:37 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Lecopzer Chen <lecopzer.chen@...iatek.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        tglx@...utronix.de, lecopzer@...il.com, yj.chiang@...iatek.com,
        Julien Thierry <julien.thierry.kdev@...il.com>
Subject: Re: [PATCH] irqchip/gic-v3: Fix IPRIORITYR can't perform byte
 operations in GIC-600

On Tue, Mar 30, 2021 at 12:05:46PM +0100, Lorenzo Pieralisi wrote:
> On Tue, Mar 30, 2021 at 11:33:13AM +0100, Marc Zyngier wrote:
> > [+Lorenzo, +Julien on an actual email address]
> > 
> > On Tue, 30 Mar 2021 11:06:19 +0100,
> > Lecopzer Chen <lecopzer.chen@...iatek.com> wrote:
> > > 
> > > When pseudo-NMI enabled, register_nmi() set priority of specific IRQ
> > > by byte ops, and this doesn't work in GIC-600.
> > > 
> > > We have asked ARM Support [1]:
> > > > Please refer to following description in
> > > > "2.1.2 Distributor ACE-Lite slave interface" of GIC-600 TRM for
> > > > the GIC600 ACE-lite slave interface supported sizes:
> > > >   "The GIC-600 only accepts single beat accesses of the sizes for
> > > >   each register that are shown in the Programmers model,
> > > >   see Chapter 4 Programmer's model on page 4-102.
> > > >   All other accesses are rejected and given either an
> > > >   OKAY or SLVERR response that is based on the GICT_ERR0CTLR.UE bit.".
> > > 
> > > Thus the register needs to be written by double word operation and
> > > the step will be: read 32bit, set byte and write it back.
> > > 
> > > [1] https://services.arm.com/support/s/case/5003t00001L4Pba
> > 
> > You do realise that this link:
> > 
> > - is unusable for most people as it is behind a registration interface
> > - discloses confidential information to other people
> > 
> > I strongly suggest you stop posting such links.
> > 
> > > 
> > > Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> > > ---
> > >  drivers/irqchip/irq-gic-v3.c | 13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > > index eb0ee356a629..cfc5a6ad30dc 100644
> > > --- a/drivers/irqchip/irq-gic-v3.c
> > > +++ b/drivers/irqchip/irq-gic-v3.c
> > > @@ -440,10 +440,21 @@ static void gic_irq_set_prio(struct irq_data *d, u8 prio)
> > >  {
> > >  	void __iomem *base = gic_dist_base(d);
> > >  	u32 offset, index;
> > > +	u32 val, prio_offset_mask, prio_offset_shift;
> > >  
> > >  	offset = convert_offset_index(d, GICD_IPRIORITYR, &index);
> > >  
> > > -	writeb_relaxed(prio, base + offset + index);
> > > +	/*
> > > +	 * GIC-600 memory mapping register doesn't support byte opteration,
> > > +	 * thus read 32-bits from register, set bytes and wtire back to it.
> > > +	 */
> > > +	prio_offset_shift = (index & 0x3) * 8;
> > > +	prio_offset_mask = GENMASK(prio_offset_shift + 7, prio_offset_shift);
> > > +	index &= ~0x3;
> > > +	val = readl_relaxed(base + offset + index);
> > > +	val &= ~prio_offset_mask;
> > > +	val |= prio << prio_offset_shift;
> > > +	writel_relaxed(val, base + offset + index);
> > >  }
> > >  
> > >  static u32 gic_get_ppi_index(struct irq_data *d)
> > 
> > From the architecture spec:
> > 
> > <quote>
> > 11.1.3 GIC memory-mapped register access
> > 
> > In any system, access to the following registers must be supported:
> > 
> > [...]
> > * Byte accesses to:
> > 	- GICD_IPRIORITYR<n>.
> > 	- GICD_ITARGETSR<n>.
> > 	- GICD_SPENDSGIR<n>.
> > 	- GICD_CPENDSGIR<n>.
> > 	- GICR_IPRIORITYR<n>.
> > </quote>
> > 
> > So if GIC600 doesn't follow this architectural requirement, this is a
> > HW erratum, and I want an actual description of the HW issue together
> > with an erratum number.
> > 
> > Lorenzo, can you please investigate on your side?
> 
> Sure - I will look into it and report back.

Checked - I don't think this patch is needed so it should be dropped and
a follow-up discussion can continue in the relevant/appropriate forum -
if there is anything left to discuss.

Thanks,
Lorenzo