Re: [PATCH v17 03/12] power: reset: reboot-mode: Add support for 64 bit magic

Shivendra Pratap
2025-11-11T14:51:11Z

On 11/11/2025 12:03 AM, Bjorn Andersson wrote:
> On Mon, Nov 10, 2025 at 11:22:40PM +0530, Shivendra Pratap wrote:
>>
>>
>> On 11/10/2025 10:00 PM, Bjorn Andersson wrote:
>>> On Mon, Nov 10, 2025 at 07:15:29PM +0530, Mukesh Ojha wrote:
>>>> On Sun, Nov 09, 2025 at 08:07:16PM +0530, Shivendra Pratap wrote:
>>>>> Current reboot-mode supports a single 32-bit argument for any
>>>>> supported mode. Some reboot-mode based drivers may require
>>>>> passing two independent 32-bit arguments during a reboot
>>>>> sequence, for uses-cases, where a mode requires an additional
>>>>> argument. Such drivers may not be able to use the reboot-mode
>>>>> driver. For example, ARM PSCI vendor-specific resets, need two
>>>>> arguments for its operation – reset_type and cookie, to complete
>>>>> the reset operation. If a driver wants to implement this
>>>>> firmware-based reset, it cannot use reboot-mode framework.
>>>>>
>>>>> Introduce 64-bit magic values in reboot-mode driver to
>>>>> accommodate dual 32-bit arguments when specified via device tree.
>>>>> In cases, where no second argument is passed from device tree,
>>>>> keep the upper 32-bit of magic un-changed(0) to maintain backward
>>>>> compatibility.
>>>>>
>>>>> Update the current drivers using reboot-mode for a 64-bit magic
>>>>> value.
>>
>> [SNIP..]
>>
>>>>> + if (magic > U32_MAX)
>>>>> + return -EINVAL;
>>>>> +
>>>>> + magic_32 = magic;
>>>>> +
>>>>> syscon_rbm = container_of(reboot, struct syscon_reboot_mode, reboot);
>>>>>
>>>>> ret = regmap_update_bits(syscon_rbm->map, syscon_rbm->offset,
>>>>> - syscon_rbm->mask, magic);
>>>>> + syscon_rbm->mask, magic_32);
>>>
>>> As above, if we're no longer silently discarding bits, I think we should
>>> compare the magic against syscon_rbm->mask.
>>>
>>> No need for a local variable, just type cast after checking the validity.
>>
>> Trying to summarize below why we added these check-
>>
>> the patch in v11 used typecasting and did not have any of these checks(link below):
>> https://lore.kernel.org/all/20250717-arm-psci-system_reset2-vendor-reboots-v11-2-df3e2b2183c3@oss.qualcomm.com/
>>
>> As per below upstream review, type cast was removed and bound checks were added all-over patchset:
>> "As a general rule of thumb, code with casts is poor quality code. Try
>> to write the code without casts." -
>> https://lore.kernel.org/all/8d4a42b6-657f-4c30-8e25-4213d8d53a89@lunn.ch/
>>
>> We can revert to the typecast way. Please suggest.
>>
>
> Okay, I'm okay with Andrew's original request, stick to that for the
> nvmem case. Although I don't fancy the name "magic_32", and would prefer
> that you just call it "value" or something.

sure will make it proper wherever applicable.

>
>
> For pon and syscon however, I'm wondering why you have ignored Andrew's
> other request from that same email:
>
> """
> You might be able to go further, and validate that magic actually fits
> into the field when you consider the << pon->reason_shift.
> """
>
> Writing "if (magic > U32_MAX)" in a snippet of code where magic isn't
> allowed to be more than either 32 or 64 is misleading.
>
> For syscon, it's true that the parameter is an unsigned long, but the
> actual limit better be based on syscon_rbm->mask.

May be i was not able to interpret it correctly. Basically tried to
make sure that magic that now coming in a "u64 magic" should be passed
ahead only it its a 32 bit value.

So should i get rid of the checks done here for syscon and pon?

thanks,
Shivendra