Ulf Hansson <ulf.hansson <at> linaro.org> writes: > > On 23 May 2014 15:34, Sascha Hauer <s.hauer <at> pengutronix.de> wrote: > > The eMMC and the SD-Card specifications describe the optional SET_DSR command. > > During measurements at our lab we found that some cards implementing this feature > > having really strong driver strengts per default. This can lead to voltage peaks > > above the specification of the host on signal edges for data sent from a card to > > the host. > > > > Since availability of a given card type may be shorter than the time a certain > > hardware will be produced it is useful to have support for this command (Alternative > > would be changing termination resistors and adapting the driver strength of the > > host to the used card.) > > > > As the value of the dsr register is board specific this adds a 'dsr' devicetree > > property which is handled in mmc_of_parse. > > > > Signed-off-by: Sascha Hauer <s.hauer <at> pengutronix.de> > > --- > > Documentation/devicetree/bindings/mmc/mmc.txt | 3 +++ > > drivers/mmc/core/host.c | 3 +++ > > drivers/mmc/core/mmc.c | 4 ++++ > > drivers/mmc/core/mmc_ops.c | 17 +++++++++++++++++ > > drivers/mmc/core/mmc_ops.h | 1 + > > include/linux/mmc/card.h | 3 ++- > > include/linux/mmc/host.h | 2 ++ > > 7 files changed, 32 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt > > index 9dce540..737203e 100644 > > --- a/Documentation/devicetree/bindings/mmc/mmc.txt > > +++ b/Documentation/devicetree/bindings/mmc/mmc.txt > > <at> <at> -38,6 +38,9 <at> <at> Optional properties: > > - mmc-highspeed-ddr-1_2v: eMMC high-speed DDR mode(1.2V I/O) is supported > > - mmc-hs200-1_8v: eMMC HS200 mode(1.8V I/O) is supported > > - mmc-hs200-1_2v: eMMC HS200 mode(1.2V I/O) is supported > > +- dsr: Content of the optional driver stage register (DSR) as described > > + in JEDEC Standard No. 84-A44, 12.4: Programmable card output driver. Not > > + all MMC cards implement this register and the actual value is card specific. > > I get the impression of that this is (e)MMC specific, but this is > relevant for SD cards as well, right!? >
Yes, the feature is optional for SD memory cards but not supported by SDIO. (accordding to SDIO Simplified Specification Version 2.00) On the other hand, I've not seen an SD card that implements this feature. Just a second thought about the SD card side: as I read and understand the specs the mapping between register values and physical driver stage value is left over to the manufacturer. So the setting makes only sense for fix mounted cards like eMMC - correct me if I'm wrong. Markus > I don't find the part's that should be implemented for sd/sdio, could > we add that in this patch as well? > -- 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
