Re: [PATCH v3] mailbox: qcom-cpucp: read mbox hardware register using readq()

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 10/13/26 2:32 PM, Sivansh Gupta wrote:
> On 2026-09-30 11:55 +0200, Konrad Dybcio wrote:
>> On 9/28/26 7:29 AM, Sivansh Gupta wrote:
>>> Mailbox hardware registers are 64 bit wide, but the interrupt handler
>>> currently reads only 32 bits with readl() at offset 0x4 (upper 32
>>> bits). This returns an incorrect value, while reading using readq()
>>> returns the expected value.
>>>
>>> Use readq() to access the 64 bit register and pass the expected value
>>> to the mailbox client.
>>>
>>> Fixes: 0e2a9a03106c ("mailbox: Add support for QTI CPUCP mailbox controller")
>>> Signed-off-by: Sivansh Gupta <sivansh.gupta@oss.qualcomm.com>
>>> ---
>>> v3:
>>> - Removed references to an out of tree driver to focus on the incorrect
>>>   value returned by readl()
>>>   https://lore.kernel.org/all/93ce8588-7500-45da-9b9a-424c202590cf@oss.qualcomm.com/#t
>>>
>>> v2:
>>> - Expanded the commit message to explain why this change is required.
>>>
>>>  drivers/mailbox/qcom-cpucp-mbox.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mailbox/qcom-cpucp-mbox.c b/drivers/mailbox/qcom-cpucp-mbox.c
>>> index 862e45e8fbd5..0b584d9aad6c 100644
>>> --- a/drivers/mailbox/qcom-cpucp-mbox.c
>>> +++ b/drivers/mailbox/qcom-cpucp-mbox.c
>>> @@ -61,7 +61,7 @@ static irqreturn_t qcom_cpucp_mbox_irq_fn(int irq, void *data)
>>>  	status = readq(cpucp->rx_base + APSS_CPUCP_RX_MBOX_STAT);
>>>  
>>>  	for_each_set_bit(i, (unsigned long *)&status, cpucp->mbox.num_chans) {
>>> -		u32 val = readl(cpucp->rx_base + APSS_CPUCP_RX_MBOX_CMD(i) + APSS_CPUCP_MBOX_CMD_OFF);
>>
>> This still retains the writel() later on
> 
> This is intentional, currently the existing mbox client(s) assume 32 bits
> writes instead of 64 bits, changing to 64 bits here would require all
> mbox clients to be updated to send 64 bits.
> Currently there is only 1 upstream client (arm_scmi).
> 
>>> +		u64 val = readq(cpucp->rx_base + APSS_CPUCP_RX_MBOX_CMD(i));
>>
>> This will alter the indices of the mailbox channels, but it's ""fine""
>> because it's always zero for the existing platforms..
>>
>> Konrad
> 
> I am unsure what you mean here. The channel registers are spaced 8 bytes
> apart. In the old code, we used to read each channel's upper 32 bits
> (channel base + 4 bytes), in the new code we will be reading the entire
> 8 bytes.
> If this is not what you meant, please let me know!

You're right, please remove the leftover define

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>

Konrad