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Message-ID: <2bff9246-dd42-1c21-930f-2da2fed588f2@linaro.org>
Date:   Wed, 29 Mar 2023 01:14:22 +0300
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Subject: Re: [PATCH v4 4/5] firmware: qcom_scm: Refactor code to support
 multiple download mode
Content-Language: en-GB
To:     Mukesh Ojha <quic_mojha@quicinc.com>,
        Bjorn Andersson <andersson@kernel.org>
Cc:     agross@kernel.org, konrad.dybcio@linaro.org,
        linus.walleij@linaro.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
References: <1679935281-18445-1-git-send-email-quic_mojha@quicinc.com>
 <1679935281-18445-5-git-send-email-quic_mojha@quicinc.com>
 <20230327182324.elrxciz5vqvryp7y@ripper>
 <e342044c-dcf9-e443-5244-0990dfc59443@quicinc.com>
From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
In-Reply-To: <e342044c-dcf9-e443-5244-0990dfc59443@quicinc.com>
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Precedence: bulk

On 28/03/2023 11:18, Mukesh Ojha wrote:
> 
> 
> On 3/27/2023 11:53 PM, Bjorn Andersson wrote:
>> On Mon, Mar 27, 2023 at 10:11:20PM +0530, Mukesh Ojha wrote:
>> [..]
>>> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
>>> index 3c6c5e7..0c94429 100644
>>> --- a/drivers/firmware/qcom_scm.c
>>> +++ b/drivers/firmware/qcom_scm.c
>>> @@ -20,11 +20,11 @@
>>>   #include <linux/clk.h>
>>>   #include <linux/reset-controller.h>
>>>   #include <linux/arm-smccc.h>
>>> +#include <linux/kstrtox.h>
>>>   #include "qcom_scm.h"
>>> -static bool download_mode = 
>>> IS_ENABLED(CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT);
>>> -module_param(download_mode, bool, 0);
>>> +static u32 download_mode;
>>>   #define SCM_HAS_CORE_CLK    BIT(0)
>>>   #define SCM_HAS_IFACE_CLK    BIT(1)
>>> @@ -32,6 +32,7 @@ module_param(download_mode, bool, 0);
>>>   #define QCOM_DOWNLOAD_MODE_MASK 0x30
>>>   #define QCOM_DOWNLOAD_FULLDUMP    0x1
>>> +#define QCOM_DOWNLOAD_NODUMP    0x0
>>>   struct qcom_scm {
>>>       struct device *dev;
>>> @@ -440,8 +441,9 @@ static int __qcom_scm_set_dload_mode(struct 
>>> device *dev, bool enable)
>>>       return qcom_scm_call_atomic(__scm->dev, &desc, NULL);
>>>   }
>>> -static void qcom_scm_set_download_mode(bool enable)
>>> +static void qcom_scm_set_download_mode(u32 download_mode)
>>>   {
>>> +    bool enable = !!download_mode;
>>>       bool avail;
>>>       int ret = 0;
>>> @@ -453,7 +455,7 @@ static void qcom_scm_set_download_mode(bool enable)
>>>       } else if (__scm->dload_mode_addr) {
>>>           ret = qcom_scm_io_update_field(__scm->dload_mode_addr,
>>>                   QCOM_DOWNLOAD_MODE_MASK,
>>> -                enable ? QCOM_DOWNLOAD_FULLDUMP : 0);
>>> +                enable ? download_mode : 0);
>>
>> Afaict, with QCOM_DOWNLOAD_NODUMP as 0, this says:
>>
>>    when download_mode is non-zero, write that value, otherwise write 0
>>
>> That should be the same as "write download_mode", so you should be able
>> to drop the enable part.
>>
>>>       } else {
>>>           dev_err(__scm->dev,
>>>               "No available mechanism for setting download mode\n");
>>> @@ -1419,6 +1421,49 @@ static irqreturn_t qcom_scm_irq_handler(int 
>>> irq, void *data)
>>>       return IRQ_HANDLED;
>>>   }
>>> +
>>> +static int get_download_mode(char *buffer, const struct kernel_param 
>>> *kp)
>>> +{
>>> +    int len = 0;
>>> +
>>> +    if (download_mode == QCOM_DOWNLOAD_FULLDUMP)
>>> +        len = sysfs_emit(buffer, "full\n");
>>> +    else if (download_mode == QCOM_DOWNLOAD_NODUMP)
>>> +        len = sysfs_emit(buffer, "off\n");
>>> +
>>> +    return len;
>>> +}
>>> +
>>> +static int set_download_mode(const char *val, const struct 
>>> kernel_param *kp)
>>> +{
>>> +    u32 old = download_mode;
>>> +
>>> +    if (!strncmp(val, "full", strlen("full"))) {
>>
>> strcmp loops over the two string until they differ and/or both are
>> '\0'.
>>
>> As such, the only thing you achieve by using strncmp(.., T, strlen(T))
>> is that the code has to iterate over T twice - and you make the code
>> harder to read.
> 
> 
> If we use strcmp, i need to use "full\n" which we would not want to do.
> I think, we need to take this hit.

There is a special helper for the sysfs files. See sysfs_streq().

> 
> -- Mukesh
>>
>>> +        download_mode = QCOM_DOWNLOAD_FULLDUMP;
>>> +    } else if (!strncmp(val, "off", strlen("off"))) {
>>> +        download_mode = QCOM_DOWNLOAD_NODUMP;
>>> +    } else if (kstrtouint(val, 0, &download_mode) ||
>>> +           !(download_mode == 0 || download_mode == 1)) {
>>> +        download_mode = old;
>>> +        pr_err("unknown download mode\n");
>>
>> This will result in a lone "unknown download mode" line somewhere in the
>> kernel log, without association to any driver or any indication what the
>> unknown value was.
>>
>>    pr_err("qcom_scm: unknown download mode: %s\n", val);
>>
>> Would give both context and let the reader know right there what value
>> the code wasn't able to match.
>>
>> Regards,
>> Bjorn

-- 
With best wishes
Dmitry