Re: [PATCH] usb: dwc3: reference clock configuration

[Kathiravan T <kathirav@codeaurora.org>]

On 2021-02-15 22:28, Kathiravan T wrote:
> On 2021-02-10 11:40, Baruch Siach wrote:
>> Hi Bjorn,
>> 
>> Thanks for your review comments.
>> 
>> On Mon, Feb 08 2021, Bjorn Andersson wrote:
>>> On Mon 08 Feb 00:00 CST 2021, Baruch Siach wrote:
>>>> From: Balaji Prakash J <bjagadee@codeaurora.org>
>>>> 
>>>> DWC_USB3_GFLADJ and DWC_USB3_GUCTL registers contain options
>>>> to control the behavior of controller with respect to SOF and ITP.
>>>> The reset values of these registers are aligned for 19.2 MHz
>>>> reference clock source. This change will add option to override
>>>> these settings for reference clock other than 19.2 MHz
>>>> 
>>>> Tested on IPQ6018 SoC based CP01 board with 24MHz reference clock.
>>>> 
>>>> Signed-off-by: Balaji Prakash J <bjagadee@codeaurora.org>
>>>> [ baruch: mention tested hardware ]
>>>> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
>>>> ---
>>>>  .../devicetree/bindings/usb/dwc3.txt          |  5 ++
>>>>  drivers/usb/dwc3/core.c                       | 52 
>>>> +++++++++++++++++++
>>>>  drivers/usb/dwc3/core.h                       | 12 +++++
>>>>  3 files changed, 69 insertions(+)
>>>> 
>>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt 
>>>> b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> index 1aae2b6160c1..4ffa87b697dc 100644
>>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>>> @@ -89,6 +89,11 @@ Optional properties:
>>>>   - snps,quirk-frame-length-adjustment: Value for GFLADJ_30MHZ field 
>>>> of GFLADJ
>>>>  	register for post-silicon frame length adjustment when the
>>>>  	fladj_30mhz_sdbnd signal is invalid or incorrect.
>>>> + - snps,quirk-ref-clock-adjustment: Value for GFLADJ_REFCLK_* 
>>>> fields of GFLADJ
>>>> +	register for reference clock other than 19.2 MHz is used.
>>> 
>>> What are typical values for this property? What unit does it have? 
>>> How
>>> does it actually relate to the frequency of the reference clock?
>> 
>> Downstream codeaurora kernel (fig branch) sets 0xA87F0 for IPQ6018
>> (24MHz reference clock), and 0x49459 for IPQ5018 (60MHz). So this 
>> value
>> appears to correlates with clock rate. I have no access to DWC3
>> documentation. I only tested IPQ6018 hardware.
>> 
> 
> It will be written as (0xA87F0 << 7) retaining the 0-7 LSB value.
> I could see, BIT(23) of GFLADJ register enables the functionality of
> running SOF/ITP counters based on the reference clock. Since this bit
> is set, we need to
> compute the other fields as well i.e., from 8th bit to 31st bit.
> Finally it is derived to
> 0xA87F0 for IPQ6018.
> 

Bjorn / All,

Any comments on this? Please do suggest if this can be handled in a 
better way.


> 
>>>> + - snps,quirk-ref-clock-period: Value for REFCLKPER filed of GUCTL. 
>>>> This field
>>>> +	indicates in terms of nano seconds the period of ref_clk. To 
>>>> calculate the
>>>> +	ideal value, REFCLKPER = (1/ref_clk in Hz)*10^9.
>>> 
>>> Can't we make the dwc3 reference this clock and use clk_get_rate() 
>>> and
>>> then do this math in the driver?
>> 
>> This is doable, I believe. Though current code does not identify
>> specific clocks, as far as I can see.
>> 
>> baruch
> 
> We can mention one more clock(ref) in the USB device node and do the
> math (NSEC_PER_SEC / clk_get_rate()) in dwc3 driver.

Thanks,
Kathiravan T.
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