[PATCH 1/3] mmc: add support for power-on sequencing through DT
Ulf Hansson
ulf.hansson at linaro.org
Tue Jan 21 03:55:03 EST 2014
On 20 January 2014 20:13, Olof Johansson <olof at lixom.net> wrote:
> On Mon, Jan 20, 2014 at 09:44:23AM +0100, Ulf Hansson wrote:
>> On 20 January 2014 04:56, Olof Johansson <olof at lixom.net> wrote:
>> > This patch enables support for power-on sequencing of SDIO peripherals through DT.
>> >
>> > In general, it's quite common that wifi modules and other similar
>> > peripherals have several signals in addition to the SDIO interface that
>> > needs wiggling before the module will power on. It's common to have a
>> > reference clock, one or several power rails and one or several lines
>> > for reset/enable type functions.
>> >
>> > The binding as written today introduces a number of reset gpios,
>> > a regulator and a clock specifier. The code will handle up to 2 gpio
>> > reset lines, but it's trivial to increase to more than that if needed
>> > at some point.
>> >
>> > Implementation-wise, the MMC core has been changed to handle this during
>> > host power up, before the host interface is powered on. I have not yet
>> > implemented the power-down side, I wanted people to have a chance for
>> > reporting back w.r.t. issues (or comments on the bindings) first.
>> >
>> > I have not tested the regulator portion, since the system and module
>> > I'm working on doesn't need one (Samsung Chromebook with Marvell
>> > 8797-based wifi). Testing of those portions (and reporting back) would
>> > be appreciated.
>> >
>> > Signed-off-by: Olof Johansson <olof at lixom.net>
>> > ---
>> > Documentation/devicetree/bindings/mmc/mmc.txt | 11 +++++++
>> > drivers/mmc/core/core.c | 42 +++++++++++++++++++++++++
>> > drivers/mmc/core/host.c | 30 +++++++++++++++++-
>> > include/linux/mmc/host.h | 5 +++
>> > 4 files changed, 87 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>> > index 458b57f..962e0ee 100644
>> > --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>> > +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>> > @@ -5,6 +5,8 @@ these definitions.
>> > Interpreted by the OF core:
>> > - reg: Registers location and length.
>> > - interrupts: Interrupts used by the MMC controller.
>> > +- clocks: Clocks needed for the host controller, if any.
>> > +- clock-names: Goes with clocks above.
>> >
>> > Card detection:
>> > If no property below is supplied, host native card detect is used.
>> > @@ -30,6 +32,15 @@ Optional properties:
>> > - cap-sdio-irq: enable SDIO IRQ signalling on this interface
>> > - full-pwr-cycle: full power cycle of the card is supported
>> >
>> > +Card power and reset control:
>> > +The following properties can be specified for cases where the MMC
>> > +peripheral needs additional reset, regulator and clock lines. It is for
>> > +example common for WiFi/BT adapters to have these separate from the main
>> > +MMC bus:
>> > + - card-reset-gpios: Specify GPIOs for card reset (reset active low)
>> > + - card-external-vcc-supply: Regulator to drive (independent) card VCC
>> > + - clock with name "card_ext_clock": External clock provided to the card
>> > +
>> > *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"
>> > line levels. We choose to follow the SDHCI standard, which specifies both those
>> > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>> > index 098374b..c43e6c8 100644
>> > --- a/drivers/mmc/core/core.c
>> > +++ b/drivers/mmc/core/core.c
>> > @@ -13,11 +13,13 @@
>> > #include <linux/module.h>
>> > #include <linux/init.h>
>> > #include <linux/interrupt.h>
>> > +#include <linux/clk.h>
>> > #include <linux/completion.h>
>> > #include <linux/device.h>
>> > #include <linux/delay.h>
>> > #include <linux/pagemap.h>
>> > #include <linux/err.h>
>> > +#include <linux/gpio.h>
>> > #include <linux/leds.h>
>> > #include <linux/scatterlist.h>
>> > #include <linux/log2.h>
>> > @@ -1519,6 +1521,43 @@ void mmc_set_driver_type(struct mmc_host *host, unsigned int drv_type)
>> > mmc_host_clk_release(host);
>> > }
>> >
>> > +static void mmc_card_power_up(struct mmc_host *host)
>> > +{
>> > + int i;
>> > + struct gpio_desc **gds = host->card_reset_gpios;
>> > +
>> > + for (i = 0; i < ARRAY_SIZE(host->card_reset_gpios); i++) {
>> > + if (gds[i]) {
>> > + dev_dbg(host->parent, "Asserting reset line %d", i);
>> > + gpiod_set_value(gds[i], 1);
>> > + }
>> > + }
>> > +
>> > + if (host->card_regulator) {
>> > + dev_dbg(host->parent, "Enabling external regulator");
>> > + if (regulator_enable(host->card_regulator))
>> > + dev_err(host->parent, "Failed to enable external regulator");
>> > + }
>> > +
>> > + if (host->card_clk) {
>> > + dev_dbg(host->parent, "Enabling external clock");
>> > + clk_prepare_enable(host->card_clk);
>> > + }
>> > +
>> > + /* 2ms delay to let clocks and power settle */
>> > + mmc_delay(20);
>> > +
>> > + for (i = 0; i < ARRAY_SIZE(host->card_reset_gpios); i++) {
>> > + if (gds[i]) {
>> > + dev_dbg(host->parent, "Deasserting reset line %d", i);
>> > + gpiod_set_value(gds[i], 0);
>> > + }
>> > + }
>> > +
>> > + /* 2ms delay to after reset release */
>> > + mmc_delay(20);
>> > +}
>> > +
>> > /*
>> > * Apply power to the MMC stack. This is a two-stage process.
>> > * First, we enable power to the card without the clock running.
>> > @@ -1535,6 +1574,9 @@ void mmc_power_up(struct mmc_host *host, u32 ocr)
>> > if (host->ios.power_mode == MMC_POWER_ON)
>> > return;
>> >
>> > + /* Power up the card/module first, if needed */
>> > + mmc_card_power_up(host);
>> > +
>> > mmc_host_clk_hold(host);
>> >
>> > host->ios.vdd = fls(ocr) - 1;
>> > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
>> > index 49bc403..e6b850b 100644
>> > --- a/drivers/mmc/core/host.c
>> > +++ b/drivers/mmc/core/host.c
>> > @@ -12,14 +12,18 @@
>> > * MMC host class device management
>> > */
>> >
>> > +#include <linux/kernel.h>
>> > +#include <linux/clk.h>
>> > #include <linux/device.h>
>> > #include <linux/err.h>
>> > +#include <linux/gpio/consumer.h>
>> > #include <linux/idr.h>
>> > #include <linux/of.h>
>> > #include <linux/of_gpio.h>
>> > #include <linux/pagemap.h>
>> > #include <linux/export.h>
>> > #include <linux/leds.h>
>> > +#include <linux/regulator/consumer.h>
>> > #include <linux/slab.h>
>> > #include <linux/suspend.h>
>> >
>> > @@ -312,7 +316,7 @@ int mmc_of_parse(struct mmc_host *host)
>> > u32 bus_width;
>> > bool explicit_inv_wp, gpio_inv_wp = false;
>> > enum of_gpio_flags flags;
>> > - int len, ret, gpio;
>> > + int i, len, ret, gpio;
>> >
>> > if (!host->parent || !host->parent->of_node)
>> > return 0;
>> > @@ -415,6 +419,30 @@ int mmc_of_parse(struct mmc_host *host)
>> > if (explicit_inv_wp ^ gpio_inv_wp)
>> > host->caps2 |= MMC_CAP2_RO_ACTIVE_HIGH;
>> >
>> > + /* Parse card power/reset/clock control */
>>
>> I would like us to prevent to open up for confusion with the "eMMC hw
>> reset" when adding this. Unless we are able to combine them in some
>> way?
>>
>> Could we maybe add some more comments about in what scenarios this DT
>> property would be useful?
>
> Ok, can do. How about something like:
>
> /*
> * Some cards need separate power/reset/clock control from the main
> * MMC/SDIO bus. Parse the description of those controls so we can
> * power on the card before the host controller.
> */
>
>
>> > + if (of_find_property(np, "card-reset-gpios", NULL)) {
>> > + struct gpio_desc *gpd;
>> > + for (i = 0; i < ARRAY_SIZE(host->card_reset_gpios); i++) {
>> > + gpd = devm_gpiod_get_index(host->parent, "card-reset", i);
>> > + if (IS_ERR(gpd))
>> > + break;
>> > + gpiod_direction_output(gpd, 0);
>> > + host->card_reset_gpios[i] = gpd;
>> > + }
>> > +
>> > + gpd = devm_gpiod_get_index(host->parent, "card-reset", ARRAY_SIZE(host->card_reset_gpios));
>> > + if (!IS_ERR(gpd)) {
>> > + dev_warn(host->parent, "More reset gpios than we can handle");
>> > + gpiod_put(gpd);
>> > + }
>> > + }
>> > +
>> > + host->card_clk = of_clk_get_by_name(np, "card_ext_clock");
>>
>> of_clk_get_by_name relies on COMMON_CLK, is that really what you want here?
>>
>> > + if (IS_ERR(host->card_clk))
>> > + host->card_clk = NULL;
>> > +
>> > + host->card_regulator = regulator_get(host->parent, "card-external-vcc");
>>
>> Is the above regulator related to host->ocr_avail mask? Could the
>> above regulator be replaced by vmmc?
>
> I have to admit that I don't know MMC as well as I could, but OCR seems to be
> something that's between the driver/controller/device, not related to external
> power control in this case?
This is related to the power of the card, typically external
regulators controlled by the host driver.
Both the card and the host supports a voltage range. This range is
exactly what the OCR mask describes. At initialization of the card,
the host ocr is validated against the card ocr.
>
>> At the moment host drivers uses mmc_regulator_get_supply(), which
>> fetches regulators called "vmmc" and "vqmmc". It is also common to
>> have these defined in DT like "vmmc-supply". This has not been
>> properly documented for most host cases, and we should fix that. I
>> also think it would make sense to include these in the documentation
>> for the common mmc bindings, instead of host specific bindings.
>
> Hm, I had been of the impression that the vmmc stuff is to control
> power/voltage on the signal lines, not for external card power. Still, even in
> that case there's need for the reset line handling and clock control.
vmmc: the power to the card.
vqmmc: the I/O voltage levels (for the signal lines).
Regarding reset, I agree, those seems to be needed.
Regarding clock control. I suppose you are referring to separate
external clocks, not affecting the SDIO/SD/MMC interface speed!?
That could make sense, but still I wonder how those shall be handled
in a fine grained power management setup. In other words, when shall
those be gated/ungated? Is the mmc core able to take the correct
decision about these?
Kind regards
Uffe
>
> I'll take a look and see if there's a way to handle that in a properly
> sequenced way and still use the same regulator.
>
>
> -Olof
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