[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20140704075710.GN31996@lukather>
Date: Fri, 4 Jul 2014 09:57:10 +0200
From: Maxime Ripard <maxime.ripard@...e-electrons.com>
To: Mark Rutland <mark.rutland@....com>
Cc: Dan Williams <dan.j.williams@...el.com>,
Vinod Koul <vinod.koul@...el.com>,
"andriy.shevchenko@...el.com" <andriy.shevchenko@...el.com>,
Arnd Bergmann <arnd@...db.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"zhuzhenhua@...winnertech.com" <zhuzhenhua@...winnertech.com>,
"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
"kevin.z.m.zh@...il.com" <kevin.z.m.zh@...il.com>,
"sunny@...winnertech.com" <sunny@...winnertech.com>,
"shuge@...winnertech.com" <shuge@...winnertech.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10 2/2] dmaengine: sun6i: Add driver for the Allwinner
A31 DMA controller
Hi Mark,
On Tue, Jul 01, 2014 at 01:48:52PM +0100, Mark Rutland wrote:
> On Tue, Jul 01, 2014 at 08:21:19AM +0100, Maxime Ripard wrote:
> > On Mon, Jun 30, 2014 at 04:33:05PM +0100, Mark Rutland wrote:
> > > On Mon, Jun 30, 2014 at 04:19:06PM +0100, Maxime Ripard wrote:
> > > > On Mon, Jun 30, 2014 at 03:20:54PM +0100, Mark Rutland wrote:
> > > > > Hi Maxime,
> > > > >
> > > > > On Mon, Jun 30, 2014 at 02:20:54PM +0100, Maxime Ripard wrote:
> > > > > > The Allwinner A31 has a 16 channels DMA controller that it shares with the
> > > > > > newer A23. Although sharing some similarities with the DMA controller of the
> > > > > > older Allwinner SoCs, it's significantly different, I don't expect it to be
> > > > > > possible to share the driver for these two.
> > > > > >
> > > > > > The A31 Controller is able to memory-to-memory or memory-to-device transfers on
> > > > > > the 16 channels in parallel.
> > > > > >
> > > > > > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> > > > > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > > > > > ---
> > > > > > drivers/dma/Kconfig | 8 +
> > > > > > drivers/dma/Makefile | 1 +
> > > > > > drivers/dma/sun6i-dma.c | 1058 +++++++++++++++++++++++++++++++++++++++++++++++
> > > > > > 3 files changed, 1067 insertions(+)
> > > > > > create mode 100644 drivers/dma/sun6i-dma.c
> > > > >
> > > > > [...]
> > > > >
> > > > > > + sdc->clk = devm_clk_get(&pdev->dev, NULL);
> > > > > > + if (IS_ERR(sdc->clk)) {
> > > > > > + dev_err(&pdev->dev, "No clock specified\n");
> > > > > > + return PTR_ERR(sdc->clk);
> > > > > > + }
> > > > > > +
> > > > > > + mux = clk_get(NULL, "ahb1_mux");
> > > > > > + if (IS_ERR(mux)) {
> > > > > > + dev_err(&pdev->dev, "Couldn't get AHB1 Mux\n");
> > > > > > + return PTR_ERR(mux);
> > > > > > + }
> > > > > > +
> > > > > > + pll6 = clk_get(NULL, "pll6");
> > > > > > + if (IS_ERR(pll6)) {
> > > > > > + dev_err(&pdev->dev, "Couldn't get PLL6\n");
> > > > > > + clk_put(mux);
> > > > > > + return PTR_ERR(pll6);
> > > > > > + }
> > > > >
> > > > > I'm slightly confused. The binding listed a single unnamed clock (the
> > > > > AHB clock). What is going on here?
> > > >
> > > > The device itself needs only a single clock to work...
> > > >
> > > > >
> > > > > > + ret = clk_set_parent(mux, pll6);
> > > > > > + clk_put(pll6);
> > > > > > + clk_put(mux);
> > > > > > +
> > > > > > + if (ret) {
> > > > > > + dev_err(&pdev->dev, "Couldn't reparent AHB1 on PLL6\n");
> > > > > > + return ret;
> > > > > > + }
> > > > >
> > > > > Why do we need to reparent the mux?
> > > >
> > > > ... but will function only if this clock is derived from PLL6.
> > >
> > > Ok, but _why_ is that the case? Could we at least have a comment for
> > > that?
> >
> > I have no idea, sorry.
>
> Oh no :(
>
> Where did this requirement turn up? Did an issue crop up in testing and
> using PLL6 just happened to work, or does some manual somewhere say that
> the device must have its clock derived from PLL6 without further
> explanation?
I first tried with the default clocks (the 24MHz oscillator) and only
transfers to devices and/or SRAM we working, but transfers from/to the
DRAM were not. Switching to PLL6 was making everything work fine. It
seems to be a bug in the A31 itself, but I don't have much details
yet.
> Does PLL6 drive some other clock that the DMA clock needs to stay in
> sync with, possibly?
PLL6 also drives some peripherals directly yes (such as the MMC or the
SPI controllers), but since I tested this using the SPI, with the main
oscillator as a source for both, I don't think it's related to
that. Or at least, not as directly related as what you were
suggesting.
>
> > > Where does the driver get the named clocks from if they aren't provided
> > > on the device node? Is there a clock-ranges somewhere?
> >
> > No, it just looks up the global clock name.
>
> Ok.
>
> > > It feels a little fragile to rely on the organisation of the clock tree
> > > and the naming thereof. If the IP block is ever reused on an SoC with a
> > > different clock tree layout then we have to handle things differently.
> >
> > What do you suggest then?
>
> I will admit that I don't have a better suggestion.
>
> Without knowing which particular constraint on the mux parent clock we
> care about it's difficult to suggest anything useful.
Well, I first made it into the mach- directory, and then was told to
move it in the driver itself, so we're kind of running out of options
:)
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)
Powered by blists - more mailing lists