linux-kernel - Re: [PATCH] soc: qcom: llcc: Add llcc device availability check

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Date: Mon, 26 Feb 2024 16:02:33 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Sahil Chandna <quic_chandna@...cinc.com>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>
CC: <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] soc: qcom: llcc: Add llcc device availability check



On 2/22/2024 11:37 PM, Sahil Chandna wrote:
> On 2/20/2024 5:58 PM, Mukesh Ojha wrote:
>> When llcc driver is enabled  and llcc device is not
>> physically there on the SoC, client can get
>> -EPROBE_DEFER on calling llcc_slice_getd() and it
>> is possible they defer forever.
>>
>> Let's add a check device availabilty and set the
>> appropriate applicable error in drv_data.
>>
>> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
>> ---
>>   drivers/soc/qcom/llcc-qcom.c | 23 ++++++++++++++++++++++-
>>   1 file changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/soc/qcom/llcc-qcom.c b/drivers/soc/qcom/llcc-qcom.c
>> index 4ca88eaebf06..cb336b183bba 100644
>> --- a/drivers/soc/qcom/llcc-qcom.c
>> +++ b/drivers/soc/qcom/llcc-qcom.c
>> @@ -769,6 +769,27 @@ static const struct qcom_sct_config x1e80100_cfgs 
>> = {
>>   };
>>   static struct llcc_drv_data *drv_data = (void *) -EPROBE_DEFER;
>> +static DEFINE_MUTEX(dev_avail);
> what is the requirement for mutex lock here? Since we are only trying to 
> find if node present or not

I was trying to avoid two parallel call from llcc_slice_getd() calling
parallel call to of_find_node_by_name() as it should be one time search 
for device presence to find a node and check if device is present or
not.

-Mukesh

>> +
>> +static bool is_llcc_device_available(void)
>> +{
>> +    static struct llcc_drv_data *ptr;
>> +
>> +    mutex_lock(&dev_avail);
>> +    if (!ptr) {
>> +        struct device_node *node;
>> +
>> +        node = of_find_node_by_name(NULL, "system-cache-controller");
>> +        if (!of_device_is_available(node)) {
>> +            pr_warn("llcc-qcom: system-cache-controller node not 
>> found\n");
>> +            drv_data = ERR_PTR(-ENODEV);
>> +        }
>> +        of_node_put(node);
>> +        ptr = drv_data;
>> +    }
>> +    mutex_unlock(&dev_avail);
>> +    return (PTR_ERR(ptr) != -ENODEV) ? true : false;
>> +}
>>   /**
>>    * llcc_slice_getd - get llcc slice descriptor
>> @@ -783,7 +804,7 @@ struct llcc_slice_desc *llcc_slice_getd(u32 uid)
>>       struct llcc_slice_desc *desc;
>>       u32 sz, count;
>> -    if (IS_ERR(drv_data))
>> +    if (!is_llcc_device_available() || IS_ERR(drv_data))
>>           return ERR_CAST(drv_data);
>>       cfg = drv_data->cfg;
>