Date: Thu, 15 Dec 2005 08:44:44 -0800
From: Greg KH <greg@kroah.com>
To: Vitaly Wool <vwool@ru.mvista.com>
Cc: David Brownell <david-b@pacbell.net>, linux-kernel@vger.kernel.org,
       dpervushin@gmail.com, akpm@osdl.org, basicmark@yahoo.com,
       komal_shah802003@yahoo.com, stephen@streetfiresound.com,
       spi-devel-general@lists.sourceforge.net, Joachim_Jaeger@digi.com
Subject: Re: [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core
Message-ID: <20051215164444.GA14870@kroah.com>
References: <20051212182026.4e393d5a.vwool@ru.mvista.com> <20051214171842.GB30546@kroah.com> <43A05C32.3070501@ru.mvista.com> <200512141102.53599.david-b@pacbell.net> <43A1118E.9040608@ru.mvista.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <43A1118E.9040608@ru.mvista.com>
User-Agent: Mutt/1.5.11
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1069
Lines: 27

On Thu, Dec 15, 2005 at 09:47:42AM +0300, Vitaly Wool wrote:
> David Brownell wrote:
> 
> >No, "stupid drivers will suffer"; nothing new.  Just observe
> >how the ads7846 touchscreen driver does small async transfers.
> > 
> >
> One cannot allocate memory in interrupt context, so the way to go is 
> allocating it on stack, thus the buffer is not DMA-safe.
> Making it DMA-safe in thread that does the very message processing is a 
> good way of overcoming this.
> Using preallocated buffer is not a good way, since it may well be
> already used by another interrupt or not yet processed by the worker
> thread (or tasklet, or whatever).

Yes it is a good way.  That's the way USB currently works in the kernel,
and it works just fine.  It keeps the rules simple and everyone knows
what needs to be done.

thanks,

greg k-h
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/