linux-kernel - Re: [PATCH 1/6] irqchip: add the Alpine MSIX interrupt controller

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Message-ID: <20160208104407.GB4117@kwain>
Date:	Mon, 8 Feb 2016 11:44:07 +0100
From:	Antoine Tenart <antoine.tenart@...e-electrons.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	tglx@...utronix.de, jason@...edaemon.net, tsahee@...apurnalabs.com,
	rshitrit@...apurnalabs.com, thomas.petazzoni@...e-electrons.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] irqchip: add the Alpine MSIX interrupt controller

On Mon, Feb 08, 2016 at 10:32:08AM +0000, Marc Zyngier wrote:
> On 08/02/16 10:26, Antoine Tenart wrote:
> >>> +static int alpine_msix_init(struct device_node *node,
> >>> +			    struct device_node *parent)
> >>> +{
> >>> +	struct alpine_msix_data *priv;
> >>> +	struct resource res;
> >>> +	int ret;
> >>> +
> >>> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> >>> +	if (!priv)
> >>> +		return -ENOMEM;
> >>> +
> >>> +	spin_lock_init(&priv->msi_map_lock);
> >>> +
> >>> +	ret = of_address_to_resource(node, 0, &res);
> >>> +	if (ret) {
> >>> +		pr_err("Failed to allocate resource\n");
> >>> +		goto err_priv;
> >>> +	}
> >>> +
> >>> +	priv->addr_high = upper_32_bits((u64)res.start);
> >>> +	priv->addr_low = lower_32_bits(res.start) + ALPINE_MSIX_SPI_TARGET_CLUSTER0;
> >>
> >> This is a bit odd. If you always set bit 16, why isn't that reflected in
> >> the base address coming from the DT?
> > 
> > The 20 least significant bits of addr_low provide direct information
> > regarding the interrupt destination, so I thought it would be clearer
> > to have this explicitly in the driver so that we know what those bits
> > mean.
> 
> So what is this information? TARGET_CLUSTER0 is not very expressive, and
> doesn't show what the alternatives are. Could you please elaborate a bit
> on that front?

For now lots of bits are reserved, so there aren't many alternatives.
Bits [18:17] are used to set the GIC to which to route the MSI and bit
16 must be set when this target GIC is the primary GIC (bits [18:17] set
to 0x0). There aren't other options available for now (that I'm aware
of) for the target GIC configuration.

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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