From: Enrico Scholz <enrico.scholz-wttK6gPy29v+Hn7q9Vec/7NAH6kLmebB@public.gmane.org>
To: Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
Subject: Re: [i2c-mxs] Broken DMA operations from within a module
Date: Wed, 13 Feb 2013 13:28:41 +0100 [thread overview]
Message-ID: <ly8v6sieiu.fsf@ensc-virt.intern.sigma-chemnitz.de> (raw)
In-Reply-To: <20130213121450.GA17833-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org> (Russell King's message of "Wed, 13 Feb 2013 12:14:50 +0000")
Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org> writes:
>> .buf = "something",
>> ...
>> random data will be sent because buf is not DMA mapable ("something" is
>> located in the .strtab section within module memory). MXS has a memory
>> layout like
>
> DMA buffers must be located in lowmem *always*. This means placing them
> in the .data segment does not work. USB has been through this already
> and it's well known there...
Yes; I know about USB and this requirement is explicitly mentioned in
the 'struct urb' documentation. But I can not find something similar
for i2c_msg and lot of i2c drivers are working with non DMA mapable
buffers.
Enrico
prev parent reply other threads:[~2013-02-13 12:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-13 12:00 [i2c-mxs] Broken DMA operations from within a module Enrico Scholz
[not found] ` <lyehgkift9.fsf-ZECJmDZ6y6nH/BybaBJVFuwNITXz66n+UvKB7fB21xCELgA04lAiVw@public.gmane.org>
2013-02-13 12:14 ` Russell King - ARM Linux
[not found] ` <20130213121450.GA17833-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org>
2013-02-13 12:28 ` Enrico Scholz [this message]
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