[GIT PULL 1/2] SOCFPGA updates for 3.18
ulf.hansson at linaro.org
Wed Sep 10 03:42:23 PDT 2014
On 10 September 2014 10:33, Pavel Machek <pavel at denx.de> wrote:
> On Wed 2014-09-10 09:13:27, Ulf Hansson wrote:
>> On 9 September 2014 23:02, Pavel Machek <pavel at denx.de> wrote:
>> > On Tue 2014-09-09 17:02:34, Arnd Bergmann wrote:
>> >> On Tuesday 09 September 2014 16:17:56 Pavel Machek wrote:
>> >> > > Jaehoon Chung (1):
>> >> > > ARM: dts: socfpga: unuse the slot-node and deprecate the supports-highspeed for dw-mmc
>> >> > >
>> >> >
>> >> > This patch is a bad idea. It removes support for two mmc cards on a
>> >> > single controller -- configuration hardware supports and configuration
>> >> > that allows using u-SD card on mcvevk board.
>> >> >
>> >> Your objection comes too late, and to the wrong patch, since the
>> >> driver and all other users have already been changed. We had a long
>> >> discussion about this when the issue first came up, and we could
>> >> not find any example of dw-mmc actually being used in a scenario
>> >> with one controller that has multiple devices attached.
>> > Well, this is not first time I raised this. 3.17 is not yet out, so we
>> > still have chance to fix regressions without major fuss.
>> >> Apparently every user out there instead uses multiple controller
>> >> instances instead. Are you sure that the socfpga implementation
>> >> is an exception from this?
>> > Marek Vasut has the hardware. His board apprently has uSD and eMMC,
>> > and I believe it has just one controller. I'll try to get details.
>> Just wanted to highlight some of the reasons to why the earlier
>> discussion we have had, came to the conclusion to remove the slot
>> 1) The mmc core don't support multiple cards attached to the same
>> host, it never has. Also, I am not aware of any requests that
>> suggested us to add it. Due to obvious reasons from performance
>> perspective it's simply a really bad idea, that's likely also why
>> there haven't been any requests for it.
> Well, that's Linux problem, right? (And why is it bad idea, btw? The
> bandwidth will be shared between the controllers, ok, that does not
> sound too bad.)
Bandwidth is just one issue. Latency is yet another, which is probably
far worse to handle than bandwidth.
>> 2) On the host level, the support for handle multiple slots in DT for
>> dw-mmc has been broken. While dw-mmc parsed the DT nodes for slots, it
>> screwed up configurations. Thus the support for slots have never
>> worked as expected from DT point of view.
> Well, DT is supposed to describe the hardware. From your description,
> it seems that linux does not support two slots on one controller and
> DT parsing code basically ignores the slots. (Logical, if it can't
> support two slots).
> So now we are breaking DT description due to Linux limitations. Which
> a) makes it hard for any other os not having same limitation
> b) makes it hard for people to fix the limitation
> c) does not really solve anything
Yes it does, the problem in 2) gets fixed.
> d) breaks backward compatibility with old dts
According to 2), it has never worked - so we don't break anything.
> If nothing, d) should be argument not to do this.
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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