From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin O'Connor Subject: Re: [PATCH v2] QEMU fw_cfg DMA interface documentation Date: Tue, 8 Sep 2015 12:46:08 -0400 Message-ID: <20150908164608.GA9169@morn.lan> References: <1441012133-8154-1-git-send-email-markmb@redhat.com> <1441012303-8261-1-git-send-email-markmb@redhat.com> <20150902103311.5335d469@markmb_rh> <1441624109.27149.18.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1441624109.27149.18.camel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Gerd Hoffmann Cc: Marc =?iso-8859-1?Q?Mar=ED?= , Stefan Hajnoczi , linux-kernel , Drew , Laszlo , Arnd Bergmann , Rob Herring , Mark Rutland , Alexander Graf , devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org 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). -Kevin