linux-kernel - Re: [PATCH v2] QEMU fw_cfg DMA interface documentation

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Message-ID: <20150910162141.7a5f70a7@markmb_rh>
Date:	Thu, 10 Sep 2015 16:21:41 +0200
From:	Marc Marí <markmb@...hat.com>
To:	"Kevin O'Connor" <kevin@...onnor.net>
Cc:	Gerd Hoffmann <kraxel@...hat.com>,
	Stefan Hajnoczi <stefanha@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Drew <drjones@...hat.com>, Laszlo <lersek@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <rob.herring@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Graf <agraf@...e.de>, devicetree@...r.kernel.org
Subject: Re: [PATCH v2] QEMU fw_cfg DMA interface documentation

On Tue, 8 Sep 2015 12:46:08 -0400
"Kevin O'Connor" <kevin@...onnor.net> wrote:

> On Mon, Sep 07, 2015 at 01:08:29PM +0200, Gerd Hoffmann wrote:
> > > It's just simplicity. If you want to read a few times from the
> > > same field (like in ACPI tables, read the data size and then the
> > > data), you need a way to enable and disable the selector and
> > > manage the current offset for that entry. This is already
> > > provided with the "old" interface.
> > 
> > Could be handled with a 'select' control bit.  Only when set select
> > entry and reset offset to zero.
> 
> I think two features would help "round off" the new fw_cfg DMA
> proposal: add a select bit as you describe (that uses the 16 most
> significant bits of the "control" field for the "select entry" when
> the bit is set), and define a static signature (eg, "QEMU CFG") when
> reading the 64bit MMIO dma register.
> 
> Both are optional features that don't change the fundamental
> interface; I was thinking of sending them as two patches on top of
> Marc's next version of his patch series (if no one else gets to it
> first).
> 

As there will be (at least) another version, I can add those simple
changes in the next version.

Thanks
Marc
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