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

[William Zhang]

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.
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