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Date:   Thu, 3 Sep 2020 10:43:02 +0200
From:   Christoph Hellwig <>
To:     Thomas Bogendoerfer <>
Cc:     Christoph Hellwig <>,,,,,,,
        "James E.J. Bottomley" <>,, Marek Szyprowski <>,,
        Joonyoung Shim <>,,
        Kyungmin Park <>,
        Ben Skeggs <>,
        Matt Porter <>,,
        Tom Lendacky <>,
        Pawel Osciak <>,
        Mauro Carvalho Chehab <>,,,, Seung-Woo Kim <>,,
Subject: Re: [PATCH 22/28] sgiseeq: convert from dma_cache_sync to

On Tue, Sep 01, 2020 at 07:38:10PM +0200, Thomas Bogendoerfer wrote:
> this is the problem:
>        /* Always check for received packets. */
>         sgiseeq_rx(dev, sp, hregs, sregs);
> so the driver will look at the rx descriptor on every interrupt, so
> we cache the rx descriptor on the first interrupt and if there was
> $no rx packet, we will only see it, if cache line gets flushed for
> some other reason.

That means a transfer back to device ownership is missing after a
(negative) check.

> kick_tx() does a busy loop checking tx descriptors,
> with just sync_desc_cpu...
> Thomas.
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]
---end quoted text---

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