Date:   Mon, 19 Mar 2018 18:02:01 +0530
From:   Vijay Viswanath <vviswana@...eaurora.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Jeremy McNicoll <jmcnicol@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        linux-arm-msm@...r.kernel.org, georgi.djakov@...aro.org,
        asutoshd@...eaurora.org, stummala@...eaurora.org,
        venkatg@...eaurora.org, pramod.gurav@...aro.org,
        jeremymc@...hat.com, evgreen@...omium.org
Subject: Re: [PATCH V2 1/2] mmc: sdhci-msm: Add support to store supported
 vdd-io voltages



On 3/7/2018 9:42 PM, Doug Anderson wrote:
> Hi,
> 
> On Tue, Mar 6, 2018 at 11:13 PM, Vijay Viswanath
> <vviswana@...eaurora.org> wrote:
>> Hi Dough, Jeremy,
>>
>>
>> On 3/3/2018 4:38 AM, Jeremy McNicoll wrote:
>>>
>>> On 2018-03-02 10:23 AM, Doug Anderson wrote:
>>>>
>>>> Hi,
>>>>
>>>> On Sun, Feb 11, 2018 at 10:01 PM, Vijay Viswanath
>>>> <vviswana@...eaurora.org> wrote:
>>>>>
>>>>> During probe check whether the vdd-io regulator of sdhc platform device
>>>>> can support 1.8V and 3V and store this information as a capability of
>>>>> platform device.
>>>>>
>>>>> Signed-off-by: Vijay Viswanath <vviswana@...eaurora.org>
>>>>> ---
>>>>>    drivers/mmc/host/sdhci-msm.c | 38
>>>>> ++++++++++++++++++++++++++++++++++++++
>>>>>    1 file changed, 38 insertions(+)
>>>>>
>>>>> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
>>>>> index c283291..5c23e92 100644
>>>>> --- a/drivers/mmc/host/sdhci-msm.c
>>>>> +++ b/drivers/mmc/host/sdhci-msm.c
>>>>> @@ -23,6 +23,7 @@
>>>>>    #include <linux/iopoll.h>
>>>>>
>>>>>    #include "sdhci-pltfm.h"
>>>>> +#include <linux/regulator/consumer.h>
>>>>
>>>>
>>>> This is a strange sort order for this include file.  Why is it after
>>>> the local include?
>>>>
>>>>
>>>>>    #define CORE_MCI_VERSION               0x50
>>>>>    #define CORE_VERSION_MAJOR_SHIFT       28
>>>>> @@ -81,6 +82,9 @@
>>>>>    #define CORE_HC_SELECT_IN_HS400        (6 << 19)
>>>>>    #define CORE_HC_SELECT_IN_MASK (7 << 19)
>>>>>
>>>>> +#define CORE_3_0V_SUPPORT      (1 << 25)
>>>>> +#define CORE_1_8V_SUPPORT      (1 << 26)
>>>>> +
>>>>
>>>>
>>>> Is there something magical about 25 and 26?  This is a new caps field,
>>>> so I'd have expected 0 and 1.
>>>>
>>>>
>>
>> Yes, these bits are the same corresponding to the capabilities in the
>> Capabilities Register (offset 0x40). The bit positions become important when
>> capabilities register doesn't show support to some voltages, but we can
>> support those voltages. At that time, we will have to fake capabilities. The
>> changes for those are currently not yet pushed up.
>>
>>
>>>>>    #define CORE_CSR_CDC_CTLR_CFG0         0x130
>>>>>    #define CORE_SW_TRIG_FULL_CALIB                BIT(16)
>>>>>    #define CORE_HW_AUTOCAL_ENA            BIT(17)
>>>>> @@ -148,6 +152,7 @@ struct sdhci_msm_host {
>>>>>           u32 curr_io_level;
>>>>>           wait_queue_head_t pwr_irq_wait;
>>>>>           bool pwr_irq_flag;
>>>>> +       u32 caps_0;
>>>>>    };
>>>>>
>>>>>    static unsigned int msm_get_clock_rate_for_bus_mode(struct sdhci_host
>>>>> *host,
>>>>> @@ -1313,6 +1318,35 @@ static void sdhci_msm_writeb(struct sdhci_host
>>>>> *host, u8 val, int reg)
>>>>>                   sdhci_msm_check_power_status(host, req_type);
>>>>>    }
>>>>>
>>>>> +static int sdhci_msm_set_regulator_caps(struct sdhci_msm_host
>>>>> *msm_host)
>>>>> +{
>>>>> +       struct mmc_host *mmc = msm_host->mmc;
>>>>> +       struct regulator *supply = mmc->supply.vqmmc;
>>>>> +       int i, count;
>>>>> +       u32 caps = 0, vdd_uV;
>>>>> +
>>>>> +       if (!IS_ERR(mmc->supply.vqmmc)) {
>>>>> +               count = regulator_count_voltages(supply);
>>>>> +               if (count < 0)
>>>>> +                       return count;
>>>>> +               for (i = 0; i < count; i++) {
>>>>> +                       vdd_uV = regulator_list_voltage(supply, i);
>>>>> +                       if (vdd_uV <= 0)
>>>>> +                               continue;
>>>>> +                       if (vdd_uV > 2700000)
>>>>> +                               caps |= CORE_3_0V_SUPPORT;
>>>>> +                       if (vdd_uV < 1950000)
>>>>> +                               caps |= CORE_1_8V_SUPPORT;
>>>>> +               }
>>>>
>>>>
>>>> Shouldn't you be using regulator_is_supported_voltage() rather than
>>>> open coding?  Also: I've never personally worked on a device where it
>>>> was used, but there is definitely a concept floating about of a
>>>> voltage level of 1.2V.  Maybe should copy the ranges from
>>>> mmc_regulator_set_vqmmc()?
>>>>
>>>>
>>
>> regulator_is_supported_voltage() checks for a range and it also uses
>> regulator_list_voltage() internally. regulator_list_voltage() is also an
>> exported API for use by drivers AFAIK. Please correct if it is not.
> 
> Sure, regulator_list_voltage() is valid to call.  I'm not saying that
> your code is wrong or violates abstractions, just that it's
> essentially re-implementing regulator_is_supported_voltage() for very
> little gain.  Calling regulator_is_supported_voltage() is better
> because:
> 
> 1. In theory, it should generate less code.  Sure, it might loop twice
> with the current implementation of regulator_is_supported_voltage(),
> but for a non-time-critical section like this smaller code is likely
> better than faster code (decreases kernel size / uses up less cache
> space, etc).
> 
> 2. If regulator_is_supported_voltage() is ever improved to be more
> efficient you'll get that improvement automatically.  If someone
> happened to source vqmmc from a PWM regulator, for instance, trying to
> enumerate all voltages like this would be a disaster.
> 
> 3. Code will be simpler to understand.
> 
> You can replace your whole loop with:
> 
> if (regulator_is_supported_voltage(mmc->supply.vqmmc, 1700000, 1950000))
>    caps |= CORE_1_8V_SUPPORT
> if (regulator_is_supported_voltage(mmc->supply.vqmmc, 2700000, 3600000))
>    caps |= CORE_3_0V_SUPPORT
> 
> 
>>>> Also: seems like you should have some way to deal with "caps" ending
>>>> up w/ no bits set.  IIRC you can have a regulator that can be enabled
>>>> / disabled but doesn't list a voltage, so if someone messed up their
>>>> device tree you could end up in this case.  Should you print a
>>>> warning?  ...or treat it as if we support "3.0V"?  ...or ?  I guess it
>>>> depends on how do you want patch #2 to behave in that case.
>>>
>>>
>>> Both, initialize it to sane value and print something.  This way at
>>> least you have a good chance of booting and not hard hanging and you
>>> are given a reasonable message indicating what needs to be fixed.
>>>
>>> -jeremy
>>>

Its good to add a warning, but initializing it to some value might not 
be appropriate. It will be better to leave it blank and if caps doesn't 
have any of 1.8V/3V, better to not enable IO_PAD_PWR_SWITCH_EN.

>>>>
>>>>
>>>>> +       }
>>>>
>>>>
>>>> How should things behave if vqmmc is an error?  In that case is it
>>>> important to not set "CORE_IO_PAD_PWR_SWITCH_EN" in patch set #2?
>>>> ...or should you set "CORE_IO_PAD_PWR_SWITCH_EN" but then make sure
>>>> you don't set "CORE_IO_PAD_PWR_SWITCH"?
>>>>
>>>>
>>
>> Thanks for the suggestion. If the regulators exit and doesn't list the
>> voltages, then I believe initialization itself will not happen. We will not
>> have any available ocr and in sdhci_setup_host it should fail.
>> But these enhancements can be incorporated. Since this patch is already
>> acknowledged, I will incorporate these changes in a subsequent patch.
> 
> It's already acknowledged?  I saw that your RFC was acknowledged by
> Adrian Hunter but then you didn't include that tag in the posting of
> v2, so I assumed for some reason it no longer applied.  If you're
> thinking that Ulf would be the one to apply this patch, he probably
> doesn't know that it's Acked either.
> 
> Perhaps Adrian or Ulf can give direction for how they see this patch proceeding.
> 
> 

Since I put up V2 anyway, I will include your suggestions and put V3. My 
mistake, I didn't notice the ACK was for RFC.

>>>>> +       msm_host->caps_0 |= caps;
>>>>> +       pr_debug("%s: %s: supported caps: 0x%08x\n", mmc_hostname(mmc),
>>>>> +                       __func__, caps);
>>>>> +
>>>>> +       return 0;
>>>>> +}
>>>>> +
>>>>> +
>>>>>    static const struct of_device_id sdhci_msm_dt_match[] = {
>>>>>           { .compatible = "qcom,sdhci-msm-v4" },
>>>>>           {},
>>>>> @@ -1530,6 +1564,10 @@ static int sdhci_msm_probe(struct platform_device
>>>>> *pdev)
>>>>>           ret = sdhci_add_host(host);
>>>>>           if (ret)
>>>>>                   goto pm_runtime_disable;
>>>>> +       ret = sdhci_msm_set_regulator_caps(msm_host);
>>>>> +       if (ret)
>>>>> +               dev_err(&pdev->dev, "%s: Failed to set regulator caps:
>>>>> %d\n",
>>>>> +                               __func__, ret);
>>>>
>>>>
>>>> Why do you need __func__ here?  You're already using dev_err(), that
>>>> gives an idea of where we are.
>>>>
>>
>> dev_err() doesn't give information of where it is getting called.
> 
> It gives you the driver and the error message should be unique to the
> driver and easy to find.  Including "__func__ in messages like this is
> discouraged unless you are in a context where you somehow can't get
> access to the device pointer.  I suppose ultimately it's up the the
> maintainer for individual cases but overall I've seen this to be a
> consistently applied rule in the kernel.
> 
> In any case, why would this particular print be special that it should
> include __func__ but all others (in this file, or in dev_err in
> general) shouldn't?
> 
> 
>>>>>           pm_runtime_mark_last_busy(&pdev->dev);
>>>>>           pm_runtime_put_autosuspend(&pdev->dev);
>>>>> --
>>>>>    Qualcomm India Private Limited, on behalf of Qualcomm Innovation
>>>>> Center, Inc.
>>>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>>>>> Linux Foundation Collaborative Project.
>>>>>
>>>>> --
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>>>
>>>
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>>
>>
>> Thanks,
>> Vijay
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> 

Thanks,
Vijay

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