linux-kernel - Re: [PATCHv7 10/12] iommu/tegra: smmu: allow duplicate ASID wirte

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Message-ID: <52AF5249.6050802@wwwdotorg.org>
Date:	Mon, 16 Dec 2013 12:19:37 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Hiroshi Doyu <hdoyu@...dia.com>, swarren@...dia.com,
	will.deacon@....com, grant.likely@...aro.org,
	thierry.reding@...il.com, robherring2@...il.com, joro@...tes.org
CC:	mark.rutland@....com, devicetree@...r.kernel.org,
	lorenzo.pieralisi@....com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, galak@...eaurora.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv7 10/12] iommu/tegra: smmu: allow duplicate ASID wirte

On 12/12/2013 12:57 AM, Hiroshi Doyu wrote:
> The device, which belongs to the same ASID, can try to enable the same
> ASID as the other swgroup devices. This should be allowed but just
> skip the actual register write. If the write value is different, it
> will return -EINVAL.

I guess this simplifies the body of the code a lot. Given this, I would
revise the code I suggested in response to a previous patch, to
something more like:

		offs = HWGRP_ASID_REG(i);
		val = smmu_read(smmu, offs);
		if (on) {
			if (WARN_ON(val && val != new_val))
				return -ENODEV;
			memcpy(c->hwgrp, map, sizeof(u64));
		} else {
			WARN_ON(val);
		}
		smmu_write(smmu, val, offs);

> +			if (val) {
> +				if (WARN_ON(val != mask))
> +					return -EINVAL;
> +				goto skip;

That means that:

a) No error is returned when the ASIDs don't match. Surely you still
want to return an error?

b) "skip" skips setting up all HWGRP IDs for the device, whereas perhaps
only 1 was shared yet the rest still need to be set up. If you really do
want to ignore the error, then surely you want "continue;" here not
"goto skip;"?

> +			}
...
> +skip:
>  	return 0;

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