Date: Fri, 11 Mar 2016 16:48:26 +0530
From: Vinod Koul <vinod.koul@intel.com>
To: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>,
        Dan Williams <dan.j.williams@intel.com>, dmaengine@vger.kernel.org,
        Chen-Yu Tsai <wens@csie.org>, linux-sunxi@googlegroups.com,
        Emilio =?iso-8859-1?Q?L=F3pez?= <emilio@elopez.com.ar>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dma: sun4i: expose block size and wait cycle
 configuration to DMA users
Message-ID: <20160311111825.GC11154@localhost>
References: <1457344771-12946-1-git-send-email-boris.brezillon@free-electrons.com>
 <20160307145429.GG11154@localhost>
 <20160307160857.577bb04d@bbrezillon>
 <20160307203024.GD8418@lukather>
 <20160308025547.GI11154@localhost>
 <20160309120627.67612b1d@bbrezillon>
 <20160311062607.GP11154@localhost>
 <20160311104552.23e06a16@bbrezillon>
 <20160311100902.GY11154@localhost>
 <20160311105549.GZ8418@lukather>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature"; boundary="HCdXmnRlPgeNBad2"
Content-Disposition: inline
In-Reply-To: <20160311105549.GZ8418@lukather>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3787
Lines: 98


--HCdXmnRlPgeNBad2
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, Mar 11, 2016 at 11:55:49AM +0100, Maxime Ripard wrote:
> On Fri, Mar 11, 2016 at 03:39:02PM +0530, Vinod Koul wrote:
> > On Fri, Mar 11, 2016 at 10:45:52AM +0100, Boris Brezillon wrote:
> > > On Fri, 11 Mar 2016 11:56:07 +0530
> > > Vinod Koul <vinod.koul@intel.com> wrote:
> > >=20
> > > > On Wed, Mar 09, 2016 at 12:06:27PM +0100, Boris Brezillon wrote:
> > > > > On Tue, 8 Mar 2016 08:25:47 +0530
> > > > > Vinod Koul <vinod.koul@intel.com> wrote:
> > > > > >=20
> > > > > > Why does dmaengine need to wait? Can you explain that
> > > > >=20
> > > > > I don't have an answer for that one, but when I set WAIT_CYCLES t=
o 1
> > > > > for the NAND use case it does not work. So I guess it is somehow
> > > > > related to how the DRQ line is controlled on the device side...
> > > >=20
> > > > Is the WAIT cycle different for different usages or same for all
> > > > usages/channels?
> > > >=20
> > >=20
> > > In Allwinner BSP they adapt it on a per slave device basis, but since
> > > DMA channels are dynamically allocated, you can't know in advance whi=
ch
> > > physical channel will be attached to a specific device.
> >=20
> > And we have the correct values availble in datasheet for all usages
>=20
> No, we don't.
>=20
> If you look at the datasheet in question, page 169.
> https://github.com/allwinner-zh/documents/blob/master/A20/A20_User_Manual=
_v1.4_20150510.pdf
>=20
> This is the only documentation we have. And as you can see, it is very
> sparse (and that's an understament).
>=20
> So we cannot make that assumption, so far the values have been found
> through trial and error for the devices in question.
>=20
> > > Another option I considered was adding a new cell to the sun4i DT
> > > binding to encode these WAIT_CYCLES and BLOCK_SIZE information. But I=
'm
> > > not sure adding that to the DT is a good idea (not to mention that it
> > > would break DT ABI again, and given the last discussions on this topi=
c,
> > > I'm not sure it's a good idea :-/).
> >=20
> > Yes i was veering towards DT as well. This is a new property so ABI rul=
es
> > wont break as long as driver still works with old properties.
>=20
> Yeah, we can always default to our current hardcoded value if the
> property is missing. And since no-one is using the engine at the
> moment anyway, so it's not really a big deal.
>=20
> > But this nees to be property for clients and not driver. Client can then
> > program these
>=20
> Yes, totally. The question here is how the clients give that
> information to the driver.

For this part am not worried. If we can generalize this then we add to
dma_slave_config. Otherwise an exported symbol from driver should be fine.


--=20
~Vinod

--HCdXmnRlPgeNBad2
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=tqP9
-----END PGP SIGNATURE-----

--HCdXmnRlPgeNBad2--