linux-kernel - Re: [PATCH v11 1/4] firmware: qcom: scm: provide a read-modify-write function

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Date: Tue, 20 Feb 2024 14:39:23 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
CC: <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 v11 1/4] firmware: qcom: scm: provide a read-modify-write
 function



On 2/17/2024 12:09 AM, Bjorn Andersson wrote:
> On Mon, Jan 08, 2024 at 08:57:31PM +0530, Mukesh Ojha wrote:
>> It was realized by Srinivas K. that there is a need of
> 
> "need" is a strong word for this functionality, unless there's some use
> case that I'm missing.

I would rather say as below,

""
It is possible that different bits of a secure register is used
for different purpose and currently, there is no such available
function from SCM driver to do that; one similar usage was pointed
by Srinivas K. inside pinctrl-msm where interrupt configuration
register lying in secure region and written via read-modify-write operation.

Export qcom_scm_io_rmw() to do read-modify-write operation on secure 
register and reuse it wherever applicable.


""
> 
>> read-modify-write scm exported function so that it can
>> be used by multiple clients.
>>
>> Let's introduce qcom_scm_io_rmw() which masks out the bits
>> and write the passed value to that bit-offset.
>>
>> Suggested-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
>> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
>> Tested-by: Kathiravan Thirumoorthy <quic_kathirav@...cinc.com> # IPQ9574 and IPQ5332
>> ---
>>   drivers/firmware/qcom/qcom_scm.c       | 26 ++++++++++++++++++++++++++
>>   include/linux/firmware/qcom/qcom_scm.h |  1 +
>>   2 files changed, 27 insertions(+)
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index 520de9b5633a..25549178a30f 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -19,6 +19,7 @@
>>   #include <linux/of_irq.h>
>>   #include <linux/of_platform.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/spinlock.h>
>>   #include <linux/reset-controller.h>
>>   #include <linux/types.h>
>>   
>> @@ -41,6 +42,8 @@ struct qcom_scm {
>>   	int scm_vote_count;
>>   
>>   	u64 dload_mode_addr;
>> +	/* Atomic context only */
>> +	spinlock_t lock;
>>   };
>>   
>>   struct qcom_scm_current_perm_info {
>> @@ -481,6 +484,28 @@ static int qcom_scm_disable_sdi(void)
>>   	return ret ? : res.result[0];
>>   }
>>   
>> +int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val)
>> +{
>> +	unsigned int old, new;
>> +	int ret;
>> +
>> +	if (!__scm)
>> +		return -EINVAL;
>> +
>> +	spin_lock(&__scm->lock);
> 
> Please express that this lock is just for create mutual exclusion
> between rmw operations, nothing else.
> 
> Also please make a statement why this is desirable and/or needed.

Sure.

However, i was thinking of reusing existing scm_query_lock with rename
which is used only during boot up in __get_convention() .

-Mukesh
> 
> Regards,
> Bjorn
> 
>> +	ret = qcom_scm_io_readl(addr, &old);
>> +	if (ret)
>> +		goto unlock;
>> +
>> +	new = (old & ~mask) | (val & mask);
>> +
>> +	ret = qcom_scm_io_writel(addr, new);
>> +unlock:
>> +	spin_unlock(&__scm->lock);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(qcom_scm_io_rmw);
>> +
>>   static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>>   {
>>   	struct qcom_scm_desc desc = {
>> @@ -1824,6 +1849,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>   		return ret;
>>   
>>   	mutex_init(&scm->scm_bw_lock);
>> +	spin_lock_init(&scm->lock);
>>   
>>   	scm->path = devm_of_icc_get(&pdev->dev, NULL);
>>   	if (IS_ERR(scm->path))
>> diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
>> index ccaf28846054..3a8bb2e603b3 100644
>> --- a/include/linux/firmware/qcom/qcom_scm.h
>> +++ b/include/linux/firmware/qcom/qcom_scm.h
>> @@ -82,6 +82,7 @@ bool qcom_scm_pas_supported(u32 peripheral);
>>   
>>   int qcom_scm_io_readl(phys_addr_t addr, unsigned int *val);
>>   int qcom_scm_io_writel(phys_addr_t addr, unsigned int val);
>> +int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val);
>>   
>>   bool qcom_scm_restore_sec_cfg_available(void);
>>   int qcom_scm_restore_sec_cfg(u32 device_id, u32 spare);
>> -- 
>> 2.7.4
>>