Subject: Re: [PATCH V2 05/13] clk: bcm2835: Add BCM2711_CLOCK_EMMC2 support

From: Florian Fainelli <[email-masked]>
Date: Fri, 13 Sep 2019 16:02:19 -0700

On 9/13/19 12:13 AM, Matthias Brugger wrote:
> 
> 
> On 13/09/2019 03:20, Stefan Wahren wrote:
>> Am 12.09.19 um 20:52 schrieb Eric Anholt:
>>> Matthias Brugger <[email-masked]> writes:
>>>
>>>> On 13/08/2019 18:20, Stefan Wahren wrote:
>>>>> The new BCM2711 supports an additional clock for the emmc2 block.
>>>>> So add a new compatible and register this clock only for BCM2711.
>>>>>
>>>>> Signed-off-by: Stefan Wahren <[email-masked]>
>>>>> Reviewed-by: Matthias Brugger <[email-masked]>
>>>>> Acked-by: Eric Anholt <[email-masked]>
>>>>> ---
>>>>>  drivers/clk/bcm/clk-bcm2835.c | 20 +++++++++++++++++++-
>>>>>  1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
>>>>> index 21cd952..fdf672a 100644
>>>>> --- a/drivers/clk/bcm/clk-bcm2835.c
>>>>> +++ b/drivers/clk/bcm/clk-bcm2835.c
>>>>> @@ -114,6 +114,8 @@
>>>>>  #define CM_AVEODIV		0x1bc
>>>>>  #define CM_EMMCCTL		0x1c0
>>>>>  #define CM_EMMCDIV		0x1c4
>>>>> +#define CM_EMMC2CTL		0x1d0
>>>>> +#define CM_EMMC2DIV		0x1d4
>>>>>
>>>>>  /* General bits for the CM_*CTL regs */
>>>>>  # define CM_ENABLE			BIT(4)
>>>>> @@ -290,7 +292,8 @@
>>>>>  #define BCM2835_MAX_FB_RATE	1750000000u
>>>>>
>>>>>  #define SOC_BCM2835		BIT(0)
>>>>> -#define SOC_ALL			(SOC_BCM2835)
>>>>> +#define SOC_BCM2711		BIT(1)
>>>>> +#define SOC_ALL			(SOC_BCM2835 | SOC_BCM2711)
>>>>>
>>>>>  /*
>>>>>   * Names of clocks used within the driver that need to be replaced
>>>>> @@ -2003,6 +2006,16 @@ static const struct bcm2835_clk_desc clk_desc_array[] = {
>>>>>  		.frac_bits = 8,
>>>>>  		.tcnt_mux = 39),
>>>>>
>>>>> +	/* EMMC2 clock (only available for BCM2711) */
>>>>> +	[BCM2711_CLOCK_EMMC2]	= REGISTER_PER_CLK(
>>>>> +		SOC_BCM2711,
>>>>> +		.name = "emmc2",
>>>>> +		.ctl_reg = CM_EMMC2CTL,
>>>>> +		.div_reg = CM_EMMC2DIV,
>>>>> +		.int_bits = 4,
>>>>> +		.frac_bits = 8,
>>>>> +		.tcnt_mux = 42),
>>>>> +
>>>>>  	/* General purpose (GPIO) clocks */
>>>>>  	[BCM2835_CLOCK_GP0]	= REGISTER_PER_CLK(
>>>>>  		SOC_ALL,
>>>>> @@ -2238,8 +2251,13 @@ static const struct cprman_plat_data cprman_bcm2835_plat_data = {
>>>>>  	.soc = SOC_BCM2835,
>>>>>  };
>>>>>
>>>>> +static const struct cprman_plat_data cprman_bcm2711_plat_data = {
>>>>> +	.soc = SOC_BCM2711,
>>>>> +};
>>>>> +
>>>>>  static const struct of_device_id bcm2835_clk_of_match[] = {
>>>>>  	{ .compatible = "brcm,bcm2835-cprman", .data = &cprman_bcm2835_plat_data },
>>>>> +	{ .compatible = "brcm,bcm2711-cprman", .data = &cprman_bcm2711_plat_data },
>>>> Because the RPi4 FW uses bcm2838-cprman as compatible, we will need to add this
>>>> here as well.
>>> Upstream has not committed to backwards compat with Pi's firmware.  That
>>> makes the ABI requirement we get held to for upstream's DT absurd, but
>>> that's the state of things.
>>
>> We also learned from past, that's not possible to keep things downstream
>> compatible. As soon as a binding is not accepted, this wont work
>> anymore. A lot of the downstream stuff is hacky.
>>
>> For example yesterday, i learned that the thermal node is broken
>> (register is part of ring oscillator block). So do we really want to be
>> compatible with a hack? I would say: No
>>
> 
> There is always the possibility to fix this in the FW, which in many cases will
> be trivial.

In many cases, the firmware can certainly be changed to support both
downstream and upstream properties, as long as the layout is not
fundamentally incompatible obviously. If this is just a game of
compatible strings, both can be provided and it should not cause any
issues as long as you are not mixing downstream and upstream drivers for
the same purpose.
-- 
Florian

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