linux-kernel - Re: [RFC] usb: dwc3: core: set force_gen1 bit in USB31 devices if max speed is SS

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Date:   Sat, 13 May 2023 00:45:31 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "quic_ppratap@...cinc.com" <quic_ppratap@...cinc.com>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [RFC] usb: dwc3: core: set force_gen1 bit in USB31 devices if max
 speed is SS

Hi Thinh,

On 5/13/2023 12:16 AM, Thinh Nguyen wrote:
> On Fri, May 12, 2023, Krishna Kurapati wrote:
>> Currently for dwc3_usb31 devices, if maximum_speed is limited to
> 
> We usually call the controller dwc_usb3, dwc_usb31, or dwc_usb32.
> 
>> super-speed in DT, then device mode is limited to SS, but host mode
>> still works in SSP.
>>
>> The documentation for max-speed property is as follows:
>>
>> "Tells USB controllers we want to work up to a certain speed.
>> Incase  this isn't passed via DT, USB controllers should default to
>> their maximum HW capability."
>>
>> It doesn't specify that the property is only for device mode.
> 
> Since this isn't really a fix, can we rephrase the lines below
> 
>> Fix this by forcing controller supported max speed to Gen1 by
>> setting LLUCTL.Force_Gen1 bit if controller is DWC3_USB31 and
>> max speed is mentioned as SS in DT.
> 
> As follow:
> There are cases where we need to limit the host's maximum speed to
> SuperSpeed only. Use this property for host mode to contrain host's
> speed to SuperSpeed.
> 
> 
Sure, will rephrase it accordingly. Thanks for the suggestion.
>>
>> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
>> ---
>> Discussion regarding the same at:
>> https://urldefense.com/v3/__https://lore.kernel.org/all/e465c69c-3a9d-cbdb-d44e-96b99cfa1a92@quicinc.com/__;!!A4F2R9G_pg!YiQpjZIJAw-yu6gEwbKqb5nusjnKQ9dQJrulx39lQP-7JMhcNA2xd8uLJoZ_HE8SuG4Rm2uvhJTSdQ2k0fJVAxU2RWYHHg$
>>
>>   drivers/usb/dwc3/core.c | 13 +++++++++++++
>>   drivers/usb/dwc3/core.h |  4 ++++
>>   2 files changed, 17 insertions(+)
>>
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 0beaab932e7d..989dc76ecbca 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -116,6 +116,18 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
>>   	dwc->current_dr_role = mode;
>>   }
>>   
>> +static void dwc3_configure_host_speed(struct dwc3 *dwc)
>> +{
>> +	u32 reg;
>> +
>> +	if (DWC3_IP_IS(DWC31) &&
>> +	   (dwc->maximum_speed == USB_SPEED_SUPER)) {
>> +		reg = dwc3_readl(dwc->regs, DWC3_LLUCTL);
>> +		reg |= DWC3_LLUCTL_FORCE_GEN1;
>> +		dwc3_writel(dwc->regs, DWC3_LLUCTL, reg);
>> +	}
>> +}
>> +
>>   static void __dwc3_set_mode(struct work_struct *work)
>>   {
>>   	struct dwc3 *dwc = work_to_dwc(work);
>> @@ -194,6 +206,7 @@ static void __dwc3_set_mode(struct work_struct *work)
>>   
>>   	switch (desired_dr_role) {
>>   	case DWC3_GCTL_PRTCAP_HOST:
>> +		dwc3_configure_host_speed(dwc);
>  > The LLUCTL doesn't change until there's a Vcc reset. Let's just> 
initialize it once during dwc3_core_init() if the GHWPARAM indicates the
> controller is DRD or host only.
> 

I thought GCTL Core soft reset might clear this bit. That is why I 
placed it here. For device mode gadget.c takes care of limiting speed. 
So wanted to do this setting only for host mode, before we invoke host init.

Thanks for letting know that only VCC reset affects this. Will move this 
check to core init.

Regards,
Krishna,

>>   		ret = dwc3_host_init(dwc);
>>   		if (ret) {
>>   			dev_err(dwc->dev, "failed to initialize host\n");
>> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
>> index d56457c02996..29b780a58dc6 100644
>> --- a/drivers/usb/dwc3/core.h
>> +++ b/drivers/usb/dwc3/core.h
>> @@ -121,6 +121,10 @@
>>   #define DWC3_GPRTBIMAP_FS0	0xc188
>>   #define DWC3_GPRTBIMAP_FS1	0xc18c
>>   #define DWC3_GUCTL2		0xc19c
>> +#define DWC3_LLUCTL		0xd024
> 
> Please place the register according to its offset order.
> 
>> +
>> +/* Force Gen1 speed on Gen2 link */
>> +#define DWC3_LLUCTL_FORCE_GEN1	BIT(10)
>>   
>>   #define DWC3_VER_NUMBER		0xc1a0
>>   #define DWC3_VER_TYPE		0xc1a4
>> -- 
>> 2.40.0
>>
> 
> Thanks,
> Thinh