linux-kernel - Re: [PATCH v2 2/3] nvmem: qfprom: sc7280: Handle the additional power-domains vote

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Date:   Fri, 30 Jul 2021 11:25:26 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "Ravi Kumar Bokka (Temp)" <rbokka@...eaurora.org>
Subject: Re: [PATCH v2 2/3] nvmem: qfprom: sc7280: Handle the additional
 power-domains vote


On 7/29/2021 9:37 PM, Doug Anderson wrote:
> Hi,
> 
> On Thu, Jul 29, 2021 at 5:01 AM Rajendra Nayak <rnayak@...eaurora.org> wrote:
>>
>> On sc7280, to reliably blow fuses, we need an additional vote
>> on max performance state of 'MX' power-domain.
>> Add support for power-domain performance state voting in the
>> driver.
>>
>> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
>> ---
>>   drivers/nvmem/qfprom.c | 26 ++++++++++++++++++++++++++
>>   1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/nvmem/qfprom.c b/drivers/nvmem/qfprom.c
>> index 81fbad5..b5f27df 100644
>> --- a/drivers/nvmem/qfprom.c
>> +++ b/drivers/nvmem/qfprom.c
>> @@ -12,6 +12,8 @@
>>   #include <linux/mod_devicetable.h>
>>   #include <linux/nvmem-provider.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/pm_domain.h>
>> +#include <linux/pm_runtime.h>
>>   #include <linux/property.h>
>>   #include <linux/regulator/consumer.h>
>>
>> @@ -139,6 +141,9 @@ static void qfprom_disable_fuse_blowing(const struct qfprom_priv *priv,
>>   {
>>          int ret;
>>
>> +       dev_pm_genpd_set_performance_state(priv->dev, 0);
>> +       pm_runtime_put(priv->dev);
> 
> To me it feels as if this should be at the end of the function rather
> than the beginning. I guess it doesn't matter (?), but it feels wrong
> that we have writes to the register space after we're don't a
> pm_runtime_put().

Right, I was confused with this too when I saw that the other resources
(regulator/clocks) were also turned off before we write into the
register space. And then looking into the driver I realized its perhaps because
the resources are needed only for the 'raw' writes and the 'conf'
read/writes can happen regardless. I'll just fix that up and put the register
writes before we really turn off any resources to avoid confusion.

> 
> 
>> @@ -420,6 +440,12 @@ static int qfprom_probe(struct platform_device *pdev)
>>                          econfig.reg_write = qfprom_reg_write;
>>          }
>>
>> +       ret = devm_add_action_or_reset(dev, qfprom_runtime_disable, dev);
>> +       if (ret)
>> +               return ret;
>> +
>> +       pm_runtime_enable(dev);
>> +
> 
> Swap the order of the two. IOW first pm_runtime_enable(), then
> devm_add_action_or_reset(). Specifically the "_or_reset" means that if
> you fail to add the action (AKA devm_add_action() fails to allocate
> the tiny amount of memory it needs) it will actually _call_ the
> action. 

Ah, I didn't know that, thanks, I'll fix the order up and repost.

> That means that in your code if the memory allocation fails
> you'll call pm_runtime_disable() without the corresponding
> pm_runtime_enable().
> 
> 
> Other than those two issues this looks good to me. Feel free to add my
> Reviewed-by when you fix them.

Thanks.

> 
> -Doug
> 

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