[PATCH v4 00/21] ARM: support for ICP DAS LP-8x4x (with dts)

Daniel Mack daniel at zonque.org
Thu Apr 17 03:38:40 PDT 2014

On 04/16/2014 10:59 PM, Sergei Ianovich wrote:
>> Well, IIRC, I asked you to look into the MMC performance
>> regressions that you reported and see what we can do about them. I
>> currently don't have hardware to reproduce this, so I can't do it
>> myself.
> I hate to point fingers, but you promissed to refresh the code on
> several occasions. It is from 3.8 tree at the moment. The regression
> may be introduced by an error in my merging of your patches. I
> published the one I tested in one piece with the results.

Ok, well. I didn't see this as a potential reason, sorry. Point taken.

I spent some hours on this topic again now, and rebased and tested my
tree to 3.15-rc1. Pushed it here:


There's some overlap to the patches you sent, which I'll comment on
directly soon.

I'm booting my board with pxa[23]xx.dtsi taken from my tree.

Please, if you find some time, test this tree and see if you still see
the performance regression.

>> My impression is that the transisiton will only be painless if the 
>> mmp_pdma driver provides comparable performance to the existing 
>> implementation. I also still think that adding hacks to the drivers
>> to manually parse the dma properties (as in #8) brings us further
>> away from a proper solution, not closer
> No doubt about that. But the regression is not the only problem.
> Driver for video capture requires an extensive rewrite as well.

Jup, I totally see your point. I was hoping for more support from
someone with access to hardware to work on this, and possibly add the
missing bits to the DMA framework to make the hot-linking possible. This
didn't happen, which is unfortunate, so we in fact might need to
recondider on how to move forward here.

> The
> result is that a working pxa DT device is kept out of the tree and
> there is no supported DT devices in tree. So no proper examples for
> new devices and no drive-by improvements. All of this prevents rather
> than facilitates eventual DT migration of tha PXA platform.

Ok, so how about this:

1. We keep the old API around, along with compat wrappers for existing
drivers until someone finally finds time to at least test the patches
that I can only compile-test myself.

2. For platforms that don't need those exotic drivers for devices that
nobody seems to be interested in, use DT and the pxa-mmp-dma driver, and
make sure it performs as well as the old implementation.

3. Do not add hacks for DT-compatability of existing drivers to make
them work with the old DMA implementation (like your patch #7).

4. For new drivers, don't add any compat code for the old DMA
implementation but soley rely on the new DMA framework.

Does this sound suitable for you?


More information about the linux-arm-kernel mailing list