MCI bus-width host caps via device tree don't work properly for dw and imx

[Trent Piepho]

On Fri, 2015-11-13 at 11:28 +0100, Sascha Hauer wrote:
> > The mci_of_parse call will not remove the 4 and 8 bits caps.  There is
> > the same problem in imx-esdhc.c.  The other two users of mci_of_parse,
> > mxs.c and tegra-sdmmc.c, don't have this problem, since they don't set
> > any bus-width host_caps in the driver and depend on the DT or
> > platform_data to have this info.
> > 
> > With drivers split 50/50, which is the right way?  Don't have the driver
> > report what bits it supports and depend on the device tree to have that
> > information?  Or have of_mci_parse remove widths that aren't indicated
> > as supported in the DT, so that the DT can remove widths the hardware
> > indicates it supports.
> 
> I think the resulting flags should be the subset of what all components
> can do, that is (driver_flags & devicetree_flags & card_flags).
> 
> So mci_of_parse() should IMO clear the MMC_CAP_8_BIT_DATA flag if the
> bus-width property is set to 4.
> 
> You should encounter the same problem under Linux, right?

Don't have the problem on Linux.  The OF parsing works the same way, but
the dw driver stats with 0 bus-width caps, like how mxs and tegra-sdmmc
work.

The linux dw_mmc driver allows "sub-drivers" to supply caps, and the
Exynos4/5 driver adds CAP_8_BIT.  Which is probably broken, as it
doesn't add 4_BIT as well and will have the same problem with the device
tree not being able to remove bus widths.