From mboxrd@z Thu Jan  1 00:00:00 1970
From: mporter@ti.com (Matt Porter)
Date: Fri, 21 Sep 2012 15:03:12 -0400
Subject: [RFC PATCH 08/13] mmc: omap_hsmmc: limit max_segs with the EDMA
 DMAC
In-Reply-To: <20120921184721.GD31374@n2100.arm.linux.org.uk>
References: <1348152226-13588-1-git-send-email-mporter@ti.com>
 <1348152226-13588-9-git-send-email-mporter@ti.com>
 <CANfBPZ81anOy8fWgKM1PgCtB4V2pEp2x1Qi4x1uPsq7QieMN5g@mail.gmail.com>
 <20120921184721.GD31374@n2100.arm.linux.org.uk>
Message-ID: <20120921190312.GL16522@beef>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Sep 21, 2012 at 07:47:21PM +0100, Russell King wrote:
> On Fri, Sep 21, 2012 at 10:45:29PM +0530, S, Venkatraman wrote:
> > On Thu, Sep 20, 2012 at 8:13 PM, Matt Porter <mporter@ti.com> wrote:
> > > The EDMA DMAC has a hardware limitation that prevents supporting
> > > scatter gather lists with any number of segments. Since the EDMA
> > > DMA Engine driver sets the maximum segments to 16, we do the
> > > same.
> > >
> > > Note: this can be removed once the DMA Engine API supports an
> > > API to query the DMAC's segment limitations.
> > >
> > 
> > I wouldn't want to bind the properties of EDMA to omap_hsmmc as this patch
> > suggests. Why don't we have a max_segs property, which when explicitly specified
> > in DT, will override the default ?
> 
> Why not have a generic way that DMA engine can export these kinds of
> properties?

That's exactly what my note above is suggesting...

Something along the lines of:

	struct slave_sg_caps
	{
		int max_segs;	/* <0 is no limit */
	}

	struct slave_sg_cap *
	dmaengine_get_slave_sg_caps(struct dma_chan *chan);

I'm sure there are or will be other characteristics worth providing to
slave drivers.

-Matt