On 10 September 2014 10:33, Pavel Machek <pavel@xxxxxxx> wrote: > On Wed 2014-09-10 09:13:27, Ulf Hansson wrote: >> On 9 September 2014 23:02, Pavel Machek <pavel@xxxxxxx> 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 >> node. >> >> 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. > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
