Re: [PATCH v2 0/6] UHS-I support for sh_mobile_sdhi

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

On Sun, 2015-06-14 at 09:36 +0200, Geert Uytterhoeven wrote:
> On Thu, Jun 11, 2015 at 5:02 PM, Ben Hutchings
> <ben.hutchings@codethink.co.uk> wrote:
> >> I may be misunderstanding the above, if so I apologise, but I would
> >> strongly prefer to avoid an arrangement where the kernel and device tree
> >> blob (DTS/DTSI -> DTB) need to be upgrade in lock-step as this tends not to
> >> lead to a good experience for users.
> >
> > I agree.
> >
> >> My preference would be to maintain
> >> backwards and forwards compatibility and if appropriate schedule removal of
> >> such compatibility.
> > [...]
> >
> > The problem is that the 'sd-uhs-sdr50' property is interpreted by the
> > MMC core, so I think it will start trying to use this mode even if the
> > driver hasn't implemented the necessary operations.  I don't see any way
> > around that.
> 
> Can't the core check for driver capabilities?
> I'm not familiar with the MMC core, but e.g. the SPI core only tries modes
> that match both SPI master (spi_master.mode_bits) and slave (spi_device.mode).

The driver already calls mmc_of_parse(), which initialises its
capabilities based only on the device tree properties.

> > The regression is relatively minor as I think the MMC core will fall
> > back to a lower speed after failing to enable SDR50.  But it will slow
> > down probing of a card.
> 
> So it does fall back (after a while). That's good.

I think I've seen this happen but haven't *specifically* tested yet.

Ben.