On Mon, 29 Jul 2013, Guennadi Liakhovetski wrote: > Hi Stephen > > On Fri, 26 Jul 2013, Stephen Warren wrote: > > > On 07/26/2013 02:23 PM, Guennadi Liakhovetski wrote: > > > Hi Stephen > > > > > > On Fri, 26 Jul 2013, Stephen Warren wrote: > > > > > >> On 07/26/2013 09:51 AM, Guennadi Liakhovetski wrote: > > >>> Add DT properties for UHS SDR12, SDR25, SDR50, SDR104 and DDR50 modes > > >>> and > > >>> for supported by the host in DDR mode VccQ values. Adding them to DT > > >>> will > > >>> automatically enable respective MMC host capabilities. > > >> > > >>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt > > >>> b/Documentation/devicetree/bindings/mmc/mmc.txt > > >> > > >>> +- uhs-sdr12: the host supports UHS SDR12 mode > > >>> +- uhs-sdr25: the host supports UHS SDR25 mode > > >>> +- uhs-sdr50: the host supports UHS SDR50 mode > > >>> +- uhs-sdr104: the host supports UHS SDR104 mode > > >>> +- uhs-ddr50: the host supports UHS DDR50 mode > > >>> +- ddr-1v2: the host can support DDR, using 1.2V VccQ > > >>> +- ddr-1v8: the host can support DDR, using 1.8V VccQ > > >> > > >> Surely the driver for the host controller already knows this, so there's > > >> no need to represent it in DT? > > > > > > Not necessarily. One driver can handle several versions of the same chip, > > > and some versions of the chip implement some of those features, others > > > don't. > > > > Certainly. > > > > > So, your choice is really whether to specify a chip version in the > > > compatible string or these properties. > > > > There's no choice there. The compatible property needs to specify all of > > the following: > > > > * A value which describes the exact chip the IP block is in. This can be > > matched on to enable any quirks that need to be handled due to > > integration of the IP into the particular chip. This value will list the > > chip version. An example might be tegra20-sdhci. > > > > * A value which describes the IP block version (if that IP block has a > > version independent of the SoC that contains it, as e.g. a Synopsis IP > > block might). A totally made-up example might be synopsis-dwc2-1.0.0 > > > > * Various more generic values that describe the HW, and that define a n > > interface to the HW that is specific and complete enough that HW can > > program to. An example might be usb-ehci (assuming a chip that doesn't > > have so many quirks that a driver has to know more than just "it's an > > EHCI controller). > > Yes, all these certainly make sense. As far as I understand, we are still > in the process of defining good clear rules for DTs, there is an "ABI" > discussion currently running on ALKML and IIRC this is also going to be a > topic for one of coming conferences. So, hopefully we're approaching a > state of a greater clarity about DT.
A short addendum. At least with Renesas SoCs I see the situation in the following way: new SoC versions appear relatively frequently. They often re-use multiple IP blocks, drivers for which are scattered across the entire kernel. Often the difference between an IP block on SoC A and A+1 can be expressed by some integers, e.g. maximum size of addressable memory. Some other differences might never get supported by the driver. And only occasionally the new IP would get a feature, support for which is added to the driver and really modifies its behaviour. With platform data therefore you either get very similar or identical configurations, maybe some .max_frame_size will change, but the driver won't change anyway, and only in some rare cases the driver really needs to be changed. With compatibility strings we have to change _all_ Renesas drivers for _each_ SoC version even if just to add a new struct of_device_id entry. This doesn't seem very productive to me. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
