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SubjectRe: [PATCH] mmc: core: add mmc-card hardware reset enable support
On Wed, Apr 05, 2017 at 08:23:29AM +0200, Richard Leitner wrote:
> On 04/05/2017 06:40 AM, Jaehoon Chung wrote:
> > Hi,
> >
> > On 04/04/2017 11:16 PM, Richard Leitner wrote:
> >> Some eMMCs disable their hardware reset line (RST_N) by default. To enable
> >> it the host must set the corresponding bit in ECSD. An example for such
> >> a device is the Micron MTFCxGACAANA-4M.
> >>
> >> This patch adds a new mmc-card devicetree property to let the host enable
> >> this feature during card initialization.
> >>
> >> Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
> >> ---
> >> Documentation/devicetree/bindings/mmc/mmc-card.txt | 3 +++
> >> drivers/mmc/core/mmc.c | 21 +++++++++++++++++++++
> >> 2 files changed, 24 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.txt b/Documentation/devicetree/bindings/mmc/mmc-card.txt
> >> index a70fcd6..8590a40 100644
> >> --- a/Documentation/devicetree/bindings/mmc/mmc-card.txt
> >> +++ b/Documentation/devicetree/bindings/mmc/mmc-card.txt
> >> @@ -12,6 +12,9 @@ Required properties:
> >> Optional properties:
> >> -broken-hpi : Use this to indicate that the mmc-card has a broken hpi
> >> implementation, and that hpi should not be used
> >> +-enable-hw-reset : some eMMC devices have disabled the hw reset functionality
> >> + (RST_N_FUNCTION) by default. By adding this property the
> >> + host will enable it during initialization.
> >
> > As i know, RST_N_FUNCTION is controlled bit[1:0]
> > 0x0 : RST_n disabled (by default)
> > 0x1 : permanently enabled
> > 0x2 : permanently disabled
> >
> > I think that it needs to add the description about these..
>
> Ok.
>
> >>
> >> Example:
> >>
> >> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> >> index b502601..518d0e3 100644
> >> --- a/drivers/mmc/core/mmc.c
> >> +++ b/drivers/mmc/core/mmc.c
> >> @@ -1520,9 +1520,16 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
> >> int err;
> >> u32 cid[4];
> >> u32 rocr;
> >> + struct device_node *np;
> >> + bool enable_rst_n = false;
> >>
> >> WARN_ON(!host->claimed);
> >>
> >> + np = mmc_of_find_child_device(host, 0);
> >> + if (np && of_device_is_compatible(np, "mmc-card"))
> >> + enable_rst_n = of_property_read_bool(np, "enable-hw-reset");
> >> + of_node_put(np);
> >> +
> >> /* Set correct bus mode for MMC before attempting init */
> >> if (!mmc_host_is_spi(host))
> >> mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN);
> >> @@ -1810,6 +1817,20 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
> >> }
> >> }
> >>
> >> + /*
> >> + * try to enable RST_N if requested
> >> + * This is needed because some eMMC chips disable this function by
> >> + * default.
> >> + */
> >> + if (enable_rst_n) {
> >> + err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> >> + EXT_CSD_RST_N_FUNCTION, EXT_CSD_RST_N_ENABLED,
> >> + card->ext_csd.generic_cmd6_time);
> >> + if (err && err != -EBADMSG)
> >> + pr_warn("%s: Enabling RST_N feature failed\n",
> >> + mmc_hostname(card->host));
> >> + }
> >
> > If enabled hw-reset, it doesn't need to re-enable this bit.
>
> Ok. I can add a check to prevent setting it, if it is set already.
>
> > i didn't check the mmc-util..
> > If mmc-util provides the changing this, the using mmc-util is better than this.
>
> mmc-utils is providing a enable/disable hwreset feature. But as this
> setting is required for my hardware to allow rebooting it, I thought it
> would be better if it's in the kernel. So I/the hw doesn't have to
> depend on userspace tools.

Doesn't really seem like something you'd want a user to have to care
about, so in DT seems fine to me.

Rob

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