Hi John,
> But is the polarity really correct? That is, if we don't have space,
> then exit with success (the function to check for space).
You are absolutely correct, this is a mistake that I made as I was resolving
conflicts while porting this patch to iommu/next from 5.4 where I implemented
and tested it.
It should be:
> - if (!queue_full(llq))
> + if (queue_has_space(llq, n))
> what is llq->state->val?
This is an other oversight for the same reason, llq->state->val has since then
been renamed llq->val
Will fix both of these in the next revision.
Thanks and kind regards,
--Fernand
________________________________________
From: John Garry <john.ga...@huawei.com>
Sent: Tuesday, September 21, 2021 18:22
To: Sieber, Fernand; w...@kernel.org; robin.mur...@arm.com
Cc: linux-arm-ker...@lists.infradead.org; iommu@lists.linux-foundation.org;
linux-ker...@vger.kernel.org
Subject: RE: [EXTERNAL] [PATCH] iommu/arm-smmu-v3: poll cmdq until it has space
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On 21/09/2021 12:43, Fernand Sieber wrote:
> do {
I didn't follow the full logic of this change yet ...
> llq->val = READ_ONCE(cmdq->q.llq.val);
> - if (!queue_full(llq))
> + if (!queue_has_space(llq, n))
But is the polarity really correct? That is, if we don't have space,
then exit with success (the function to check for space).
> break;
>
> + /*
> + * We must return here even if there's no space, because the
> producer
> + * having moved forward could mean that the last thread
> observing the
> + * SMMU progress has allocated space in the cmdq and moved on,
> leaving
> + * us in this waiting loop with no other thread updating
> + * llq->state->val.
what is llq->state->val?
> + */
> + if (llq->prod != prod)
> + return -EAGAIN;
> +
> ret = queue_poll(&qp);
Thanks,
John
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