[PATCH] timer: bcmbca: Add Broadcom BCMBCA timer support

[William Zhang]

On 08/04/2022 01:25 PM, William Zhang wrote:
> Hi Florian,
> 
> On 08/03/2022 08:21 PM, Florian Fainelli wrote:
>>
>>
>> On 8/2/2022 5:07 PM, William Zhang wrote:
>>> Hi Rafal,
>>>
>>> On 08/01/2022 10:26 PM, Rafał Miłecki wrote:
>>>> On 2.08.2022 00:03, William Zhang wrote:
>>>>> This driver supports the peripheral block timer found on the Broadcom
>>>>> BCA SoCs. It is 30-bit up-count timer running at 50MHz and can be used
>>>>> as the system clock source such as on BCM63138.
>>>>> Signed-off-by: William Zhang <william.zhang at broadcom.com>
>>>>>
>>>>> (...)
>>>>>
>>>>> +static const struct udevice_id bcmbca_timer_ids[] = {
>>>>> +    { .compatible = "brcm,bcm-timers" },
>>>>> +    { }
>>>>> +};
>>>>> +
>>>>> +U_BOOT_DRIVER(bcmbca_timer) = {
>>>>> +    .name = "bcmbca_timer",
>>>>> +    .id = UCLASS_TIMER,
>>>>> +    .of_match = bcmbca_timer_ids,
>>>>> +    .priv_auto = sizeof(struct bcmbca_timer_priv),
>>>>> +    .probe = bcmbca_timer_probe,
>>>>> +    .ops = &bcmbca_timer_ops,
>>>>> +    .flags = DM_FLAG_PRE_RELOC,
>>>>> +};
>>>>
>>>> That "brcm,bcm-timers" seems like a really wide bidding. Is that exact
>>>> timer block guaranteed to be present on all Broadcom devices? Does it
>>>> exist e.g. on Northstar SoCs? Or old MIPS SoCs like BCM4706?
>>>>
>>> Agree I will make change to use brcm,bcmbca-timers.
>>
>> Why not change to use a compatible string that uses the first chip in 
>> which this timer block was introduced, was that 6345 or later?
>>
> I don't mind to change to 6345. That chip should support the same timer 
> block. Looks u-boot has a lot of Broadcom MIPS based chips that uses 
> 6345 in compatible string name for various blocks.
> 
>>>
>>>> It seems that even across BCMBCA devices this block may differ and may
>>>> need different bindings. Most SoCs have 4 CTL and 4 CNT registers but
>>>> some have only 3 + 3 (BCM6838 BCM60333 BCM63268).
>>> This timer driver is intended for the clock source for u-boot only so 
>>> only need the first channel. Although it could work for the old mips 
>>> based dsl chip, BCMBCA chip family support is only for the new ARM 
>>> based   chips which is stated in the BCMBA introduction patch.
>>>
>>>>
>>>> Finally could we have that binding actually documented?
>>> I don't see u-boot has binding document.  I believe it generally use 
>>> linux binding document.  I have no plan to upstream this driver to 
>>> linux. But I can put the binding info in the driver if that is the 
>>> right way to do in u-boot.
>>
>> Out of curiosity, why does u-boot require this timer as opposed to 
>> using the Cortex-A9 architected timers? Is it necessary to boot strap 
>> the A9 timers?
> Cortex-A9 has an arch timer called global timer.  But I don't see a 
> generic global timer driver in the u-boot. There is one from 
> STMicroelectronics sti-timer.c which is a a9 global timer but it is 
> implemented under STI_TIMER and default enabled for ARCH_STI. I guess we 
> can use that too when we have the clk driver(iproc clock driver) ported 
> to u-boot. Just curious, does anyone in this list know why sti timer is 
> not put under global timer config and file name?  I don't see anything 
> in that driver is sti specific. CC'ed driver maintainer Patrice as well.

Since there is already global timer support in u-boot,  I decided to use 
that for BCM63138. So I withdrew this patch and please discard.

I will also send a patch to move the sti a9 global timer to generic arm 
a9 global timer driver if Patrice agrees or I don't hear from him back 
next week.
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