linux-kernel - Re: [PATCH 1/1] irqchip/GICv2m: Add workaround for APM X-Gene GICv2m erratum

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Date:	Sat, 3 Oct 2015 14:26:50 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Duc Dang <dhdang@....com>
Cc:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Jason Cooper <jason@...edaemon.net>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/1] irqchip/GICv2m: Add workaround for APM X-Gene
 GICv2m erratum

On Fri, 2 Oct 2015 15:16:49 -0700
Duc Dang <dhdang@....com> wrote:

Hi Duc,

> APM X-Gene GICv2m implementation has an erratum where the
> MSI data needs to be the offset from the spi_start in order to
> trigger the correct MSI interrupt. This is different from the
> standard GICv2m implementation where the MSI data is the absolute
> value within the range from spi_start to (spi_start + num_spis)
> of each v2m frame.
> 
> This patch reads MSI_IIDR register (present in all GICv2m
> implementations) to identify X-Gene GICv2m implementation and
> apply workaround to change the data portion of MSI vector.
> 
> Signed-off-by: Duc Dang <dhdang@....com>
> ---
>  drivers/irqchip/irq-gic-v2m.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v2m.c b/drivers/irqchip/irq-gic-v2m.c
> index db04fc1..470972c 100644
> --- a/drivers/irqchip/irq-gic-v2m.c
> +++ b/drivers/irqchip/irq-gic-v2m.c
> @@ -43,6 +43,10 @@
>  
>  #define V2M_MSI_TYPER_NUM_SPI(x)       ((x) & V2M_MSI_TYPER_NUM_MASK)
>  
> +#define V2M_MSI_IIDR			0xFCC

Please group this with the rest of the registers.

> +/* APM X-Gene with GICv2m MSI_IIDR register value */
> +#define XGENE_GICV2M_MSI_IIDR		0x06000170
> +

Is this value guaranteed to only identify the affected implementation?
Do we have strong guarantees that a fixed implementation will not have
this value?

If not, I'd strongly suggest using a different method (compatible
string).

>  struct v2m_data {
>  	spinlock_t msi_cnt_lock;
>  	struct resource res;	/* GICv2m resource */
> @@ -98,6 +102,16 @@ static void gicv2m_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>  	msg->address_hi = (u32) (addr >> 32);
>  	msg->address_lo = (u32) (addr);
>  	msg->data = data->hwirq;
> +	/*
> +	 * APM X-Gene GICv2m implementation has an erratum where
> +	 * the MSI data needs to be the offset from the spi_start
> +	 * in order to trigger the correct MSI interrupt. This is
> +	 * different from the standard GICv2m implementation where
> +	 * the MSI data is the absolute value within the range from
> +	 * spi_start to (spi_start + num_spis).
> +	 */
> +	if (readl_relaxed(v2m->base + V2M_MSI_IIDR) == XGENE_GICV2M_MSI_IIDR)
> +		msg->data = data->hwirq - v2m->spi_start;
>  }
>  
>  static struct irq_chip gicv2m_irq_chip = {

Please add a set of flags to struct v2m_data as well as a flag
(GICV2M_NEEDS_SPI_OFFSET?) that can be checked in the compose method
(we don't needs to read the IIDR register each time we program an MSI):

	if (v2m->flags & GICV2M_NEEDS_SPI_OFFSET)
		msg->data -= v2m->spi_start;

You can set that flag from the probe function.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.
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