netdev - Re: [PATCHv2] usb: hso: obey DMA rules in tiocmget

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Message-Id: <20191017.132417.2018767014754768906.davem@davemloft.net>
Date:   Thu, 17 Oct 2019 13:24:17 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     neiljerram@...tab.net
Cc:     oneukum@...e.com, netdev@...r.kernel.org, johan@...nel.org
Subject: Re: [PATCHv2] usb: hso: obey DMA rules in tiocmget

From: Neil Jerram <neiljerram@...tab.net>
Date: Thu, 17 Oct 2019 15:50:31 +0100

> Oliver Neukum <oneukum@...e.com> writes:
> 
>> The serial state information must not be embedded into another
>> data structure, as this interferes with cache handling for DMA
>> on architectures without cache coherence..
>> That would result in data corruption on some architectures
> 
> Could you say more what you mean by "some architectures"?  I wonder if
> this is responsible for long-standing flakiness dealing with the HSO
> modem in the GTA04 phone?

Some MIPS, older sparc, etc.

I think this is documented in DMA API usage documentation under Documentation/
even.