On 14 August 2014 11:49, Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> wrote: > Hello Ulf, > > On Thu, Aug 14, 2014 at 11:26:28AM +0200, Ulf Hansson wrote: >> On 13 August 2014 17:44, Uwe Kleine-König >> <u.kleine-koenig@xxxxxxxxxxxxxx> wrote: >> > From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> >> > >> > Some (e)MMC and SD cards implement a DSR register that allows to tune >> > raise/fall times and drive strength of the CMD and DATA outputs. >> > The values to use depend on the card in use and the host. >> > It might be needed to reduce the drive strength to prevent voltage peaks >> > above the host's specification. >> > >> > Implement a 'dsr' devicetree property that allows to specify the value >> > to set the DSR to. For non-dt setups the new members of mmc_host can be >> > set by board code. >> > >> > This patch was initially authored by Sascha Hauer. It contains >> > improvements authored by Markus Niebel and Uwe Kleine-König. >> > >> > Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> >> > Signed-off-by: Markus Niebel <Markus.Niebel@xxxxxxxxxxxx> >> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> >> > --- >> > Hello, >> > >> > earlier incarnations of this patch can be found at >> > >> > http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/272983.html >> > http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/259281.html >> > >> > I need this functionallity on a machine where the default driver strength of >> > the eMMC chip is too big for the SoC. It seems to work without adapting the >> > drive strength, but the vendor reports that the DSR should be set to a certain >> > value to prevent poor signal integrity and increased wearout. >> > >> > Best regards >> > Uwe >> > >> > Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++ >> > drivers/mmc/core/host.c | 8 ++++++++ >> > drivers/mmc/core/mmc.c | 8 ++++++++ >> > drivers/mmc/core/mmc_ops.c | 21 +++++++++++++++++++++ >> > drivers/mmc/core/mmc_ops.h | 1 + >> > drivers/mmc/core/sd.c | 8 ++++++++ >> > include/linux/mmc/card.h | 3 ++- >> > include/linux/mmc/host.h | 3 +++ >> > 8 files changed, 53 insertions(+), 1 deletion(-) >> > >> > diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt >> > index 3c18001dfd5d..05bac770b4d0 100644 >> > --- a/Documentation/devicetree/bindings/mmc/mmc.txt >> > +++ b/Documentation/devicetree/bindings/mmc/mmc.txt >> > @@ -40,6 +40,8 @@ Optional properties: >> > - mmc-hs200-1_2v: eMMC HS200 mode(1.2V I/O) is supported >> > - mmc-hs400-1_8v: eMMC HS400 mode(1.8V I/O) is supported >> > - mmc-hs400-1_2v: eMMC HS400 mode(1.2V I/O) is supported >> > +- dsr: Value the card's (optional) Driver Stage Register (DSR) should be >> > + programmed with. >> >> Let's clarify that this is a 16 bit value. > ok. > >> > *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line >> > polarity properties, we have to fix the meaning of the "normal" and "inverted" >> > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c >> > index 95cceae96944..52e83f389428 100644 >> > --- a/drivers/mmc/core/host.c >> > +++ b/drivers/mmc/core/host.c >> > @@ -452,6 +452,14 @@ int mmc_of_parse(struct mmc_host *host) >> > if (of_find_property(np, "mmc-hs400-1_2v", &len)) >> > host->caps2 |= MMC_CAP2_HS400_1_2V | MMC_CAP2_HS200_1_2V_SDR; >> > >> > + if (of_find_property(np, "dsr", &len)) { >> > + u32 tmp; >> > + >> > + of_property_read_u32(np, "dsr", &tmp); >> > + host->dsr_req = 1; >> > + host->dsr = (u16)tmp; >> > + } >> > + >> >> Let's simplify the above with just: >> of_property_read_u16(np, "dsr", &host->dsr); > ok. > >> > return 0; >> > >> > out: >> > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c >> > index 793c6f7ddb04..fdc1ac1360c4 100644 >> > --- a/drivers/mmc/core/mmc.c >> > +++ b/drivers/mmc/core/mmc.c >> > @@ -162,6 +162,7 @@ static int mmc_decode_csd(struct mmc_card *card) >> > csd->read_partial = UNSTUFF_BITS(resp, 79, 1); >> > csd->write_misalign = UNSTUFF_BITS(resp, 78, 1); >> > csd->read_misalign = UNSTUFF_BITS(resp, 77, 1); >> > + csd->dsr_imp = UNSTUFF_BITS(resp, 76, 1); >> > csd->r2w_factor = UNSTUFF_BITS(resp, 26, 3); >> > csd->write_blkbits = UNSTUFF_BITS(resp, 22, 4); >> > csd->write_partial = UNSTUFF_BITS(resp, 21, 1); >> > @@ -1273,6 +1274,13 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr, >> > } >> > >> > /* >> > + * handling only for cards supporting DSR and hosts requesting >> > + * DSR configuration >> > + */ >> > + if (card->csd.dsr_imp && host->dsr_req) >> >> We don't need host->dsr_req. Instead just check host->dsr. > I think this doesn't work. What is your actual suggestion? > > if (card->csd.dsr_imp && host->dsr) > > ? The intended semantic is that if the device tree has: > > dsr = <$somevalue>; > > the DSR is written, and if there is no such property, DSR is unhandled. > If you just check for host->dsr being != 0, how to differenciate between > > dsr = <0>; I didn't think that was a valid mask? If so, you right! 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
