Re: [PATCH 5/9] ARM: dts: provide DMA config to pxamci

[Sergei Ianovich]

On Mon, 2013-12-09 at 13:34 +0400, Sergei Ianovich wrote:
> On Mon, 2013-12-09 at 10:04 +0100, Daniel Mack wrote:
> > On 12/09/2013 02:33 AM, Arnd Bergmann wrote:
> > > On Sunday 08 December 2013, Sergei Ianovich wrote:
> > >> Non-dts implementation supply required DMA channel numbers as
> > >> IORESOURCE_DMA. However, there is was no way to get them from
> > >> device tree.
> > > 
> > > I just wrote a lengthy reply to this email to explain in what ways
> > > you got it wrong, but then I saw that Daniel has already done all
> > > the work in the right way in August, so nevermind that.
> > > 
> > > It hasn't made it upstream yet, but see http://list-archives.org/2013/08/07/linux-mtd-lists-infradead-org/patch-00-20-arm-pxa-move-core-and-drivers-to-dmaengine/f/3444199144
> > > for how it's done. Maybe Daniel can comment on the status of his
> > > patches.
> > 
> > I recently rebased all my patches on top of 3.13-rc3, and will resend in
> > couple of days.
> > 
> > The real problem here is that by reworking the DMA related PXA bits, all
> > drivers have to be changed at once, and a gradual transition seems
> > impossible. For that, I was asking for help in areas where I don't have
> > any hardware to test my patches on, but unfortunately, nobody got back
> > to me yet.
> 
> Nice to have Daniel in this conversation. Your patch series is a big and
> important work. However, I am not sure I will ever land as is exactly
> for this reason.

s/I will/it will/

> DMA is a per-physical-device concept, not per-platform. Only the DMA
> controller is per-platform. This means we need to rewrite all platform
> drivers at once. This is roughly equivalent to adding a new platform
> support in one patch, which is not going to work.
> 
> In patch 08/20 in the series above, you change 10% lines of the pxa mmc
> driver. If we don't count boilerplate lines, this will amount to over
> 50%. In other word, the output is a new driver.

s/other word/other words/

> My proposal in to actually add new drivers for each platform device with
> DMA and mark new ones EXPERIMENTAL. When they receive adequate testing
> we remove the tag and mark the old one OBSOLETE. When we have a new
> driver for every device presently supported, we will drop the whole old
> series.

s/proposal in/proposal is/

> This should be very close to a gradual transition.
> 
> While we are in transition, I propose that we allow 'hackish' support
> for device tree in the existing drivers. Platform devices are declared
> in dtsi files, so when we move to a new driver we just change the
> compatible string there. Actual devices with their one dts file won't
> need any change. They will need a dtb recompile, though. This way we can
> begin a migration to device tree in pxa immediately.

s/their one/their own/

> The patch series does just that.

Sorry for noise.

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