linux-kernel - Re: [PATCH 2/3] irqchip: irq-mips-gic: Provide function to map GIC user section

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Date:	Mon, 28 Sep 2015 16:03:58 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Qais Yousef <qais.yousef@...tec.com>,
	Markos Chandras <markos.chandras@...tec.com>
CC:	linux-mips@...ux-mips.org, alex@...x-smith.me.uk,
	Alex Smith <alex.smith@...tec.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] irqchip: irq-mips-gic: Provide function to map GIC
 user section

On 28/09/15 15:16, Qais Yousef wrote:
> On 09/28/2015 11:55 AM, Marc Zyngier wrote:
>> On 28/09/15 11:11, Markos Chandras wrote:
>>
>>> +
>>> +	pfn = (gic_base_addr + USM_VISIBLE_SECTION_OFS) >> PAGE_SHIFT;
>>> +	return io_remap_pfn_range(vma, base, pfn, size,
>>> +				  pgprot_noncached(PAGE_READONLY));
>>
>> - Does this code have to be in the irqchip driver? It really feels out
>> of place, and I'd rather see a function that returns the mappable range
>> to the VDSO code, where the mapping would occur.
>>
> 
> 
> I don't think it's a good idea either for the VDSO code to know about 
> gic_base_addr. Maybe this function could be split to return the pfn and 
> let the caller do io_remap_pfn_range(). Though I think it's nice to have 
> it all there. USM stands for USer Mode - GIC wants to make some stuff 
> visible to user mode and it puts them in that special section. So it 
> makes sense to do it all there IMO.

Maybe I wasn't clear enough. My suggestion was to expose this in
the VDSO setup code:

@@ -90,8 +133,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 		goto out;
 	}
 
+	/* Map GIC user page. */
+	if (gic_size) {
+		ret = gic_map_user_section(vma, base, gic_size);
+		if (ret)
+			goto out;
+	}
+

This could easily be written as:

	if (gic_size) {
		struct resource gic_res;
		ret = gic_get_usm_range(&gic_res);
		if (ret)
			goto out;
		... and perform the mapping here...
	}

You can also rewrite the hunks above to actually get the present/size
information from the GIC. And if you have DT, you should be able to
directly find the memory region there, without involving the GIC
driver at all.

I don't really fancy having some userspace visible stuff in an
interrupt controller driver, and I tend to find it nicer to split
the responsabilities: the VDSO code deals with the userspace mapping,
and the interrupt controller deals with interrupts.

Thanks,

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