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

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Date:   Tue, 30 Mar 2021 11:33:13 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Lecopzer Chen <lecopzer.chen@...iatek.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <tglx@...utronix.de>,
        <lecopzer@...il.com>, <yj.chiang@...iatek.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>
Subject: Re: [PATCH] irqchip/gic-v3: Fix IPRIORITYR can't perform byte operations in GIC-600

[+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?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.