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

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Date:   Wed, 29 Mar 2023 13:03:09 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>
CC:     <agross@...nel.org>, <konrad.dybcio@...aro.org>,
        <linus.walleij@...aro.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v4 4/5] firmware: qcom_scm: Refactor code to support
 multiple download mode



On 3/29/2023 3:44 AM, Dmitry Baryshkov wrote:
> 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().

You are awesome !!
Thanks.

Have applied the change.

-- Mukesh
> 
>>
>> -- 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
>