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@xxxxxxxxxxx>
>> ---
>> 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.
Nonetheless you're the experts, therefore if you say it shouldn't be in
the kernel/dt I'd be fine with that too. ;-)
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