Re: [PATCH 2/8] soc: ti: add initial PRM driver with reset control support

[Suman Anna <s-anna@ti.com>]

On 8/21/19 10:10 AM, Philipp Zabel wrote:
> On Tue, 2019-08-20 at 11:47 -0500, Suman Anna wrote:
>> On 8/20/19 2:37 AM, Tero Kristo wrote:
>>> On 20.8.2019 2.01, Suman Anna wrote:
>>>> Hi Tero,
>>>>
>>>> On 8/19/19 4:32 AM, Tero Kristo wrote:
> [...]
>>>>>>> +{
>>>>>>> +    struct omap_reset_data *reset;
>>>>>>> +
>>>>>>> +    /*
>>>>>>> +     * Check if we have resets. If either rstctl or rstst is
>>>>>>> +     * non-zero, we have reset registers in place. Additionally
>>>>>>> +     * the flag OMAP_PRM_NO_RSTST implies that we have resets.
>>>>>>> +     */
>>>>>>> +    if (!prm->data->rstctl && !prm->data->rstst &&
>>>>>>> +        !(prm->data->flags & OMAP_PRM_NO_RSTST))
>>>>>>> +        return 0;
>>>>>>> +
>>>>>>> +    reset = devm_kzalloc(&pdev->dev, sizeof(*reset), GFP_KERNEL);
>>>>>>> +    if (!reset)
>>>>>>> +        return -ENOMEM;
>>>>>>> +
>>>>>>> +    reset->rcdev.owner = THIS_MODULE;
>>>>>>> +    reset->rcdev.ops = &omap_reset_ops;
>>>>>>> +    reset->rcdev.of_node = pdev->dev.of_node;
>>>>>>> +    reset->rcdev.nr_resets = OMAP_MAX_RESETS;
>>>>
>>>> Suggest adding a number of resets to prm->data, and using it so that we
>>>> don't even entertain any resets beyond the actual number of resets.
>>>
>>> Hmm why bother? Accessing a stale reset bit will just cause access to a
>>> reserved bit in the reset register, doing basically nothing. Also, this
>>> would not work for am3/am4 wkup, as there is a single reset bit at an
>>> arbitrary position.
>>
>> The generic convention seems to be defining a reset id value defined
>> from include/dt-bindings/reset/ that can be used to match between the
>> dt-nodes and the reset-controller driver.
>>
>> Philipp,
>> Any comments?
> 
> Are there only reset bits and reserved bits in the range accessible by
> [0..OMAP_MAX_RESETS] or are ther bits with another function as well?

Thanks Philipp, these are just reset bits and reserved bits.

> If the latter is the case, I would prefer enumerating the resets in a
> dt-bindings header, with the driver containing an enum -> reg/bit
> position lookup table.
> 
> In general, assuming the device tree contains no errors, this should not
> matter much, but I think it is nice if the reset driver, even with a
> misconfigured device tree, can't write into arbitrary bit fields.

Tero,
Can you add a check for this if possible?

regards
Suman

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