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Re: Any complications of using CONFIG_MIPS_UNCACHED..?

To: Ashish anand <>
Subject: Re: Any complications of using CONFIG_MIPS_UNCACHED..?
From: Ralf Baechle <>
Date: Tue, 27 May 2003 11:26:49 +0200
In-reply-to: <>
Original-recipient: rfc822;
References: <>
User-agent: Mutt/1.4.1i
On Wed, May 21, 2003 at 11:16:49AM +0530, Ashish anand wrote:

> I saw a good bit of discussion about CONFIG_MIPS_UNCACHED but
> still i am yet to know...
> If I want to use CONFIG_MIPS_UNCACHED (ignoring performance)
> what all the side-effects and any restrictions that linux should
> take care in software ?
> I observed something surprising on my R4k mips system(virtually indexed
> caches), after i use this option my driver never got status updation by
> device in transmit and receive decriptors in system memory , Irrespective
> of I (flushed+invalidate) caches or not...

Descriptors sounds like networking.  Network descriptors should usually
be stored in uncached or otherwise coherent space that is allocated
through pci_alloc_consistent anyway.  If you do that CONFIG_MIPS_UNCACHED
should not make any difference anymore.

> if i don't use CONFIG_MIPS_UNCACHED then before checking status I need to 
> (flush+invalidate) cache and whole thing works great...

That's a funny bug.  Normally the opposite behaviour would be expected for
a bug ...


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