Re: [PATCH v4 4/5] firmware: qcom_scm: Refactor code to support multiple download mode

[Mukesh Ojha <quic_mojha@quicinc.com>]

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.

-- 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