Re: [EXTERNAL] Re: [PATCH] usb: cdns3: gadget.c: Set fast access bit

[Roger Quadros <rogerq@kernel.org>]

+Pawel & Peter

On 09/05/2023 08:58, Ravi Gunasekaran wrote:
> Hi Roger,
> 
> On 05/05/23 6:02 pm, Roger Quadros wrote:
>> Hi Ravi,
>>
>> On 05/05/2023 15:13, Ravi Gunasekaran wrote:
>>> From: Aswath Govindraju <a-govindraju@ti.com>
>>>
>>> When the device port is in a low power state [U3/L2/Not Connected],
>>> accesses to usb device registers may take a long time. This could lead to
>>> potential core hang when the controller registers are accessed after the
>>> port is disabled by setting DEVDS field. Setting the fast register access
>>> bit ensures that the PHY clock is keeping up in active state.
>>>
>>> Therefore, set fast access bit to ensure the accesses to device registers
>>> are quick even in low power states.
>>>
>>> Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
>>> ---
>>>  drivers/usb/cdns3/gadget.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
>>> index fcaeab9cc1..fddc8c931a 100644
>>> --- a/drivers/usb/cdns3/gadget.c
>>> +++ b/drivers/usb/cdns3/gadget.c
>>> @@ -2321,6 +2321,9 @@ static void cdns3_gadget_config(struct cdns3_device *priv_dev)
>>>  	writel(USB_IEN_INIT, &regs->usb_ien);
>>>  	writel(USB_CONF_CLK2OFFDS | USB_CONF_L1DS, &regs->usb_conf);
>>>  
>>> +	/* Set the Fast access bit */
>>> +	writel(PUSB_PWR_FST_REG_ACCESS, &priv_dev->regs->usb_pwr);
>>> +
>>
>> Should this be done in cdns3_gadget_udc_start() so it is symmetric?
>>
> 
> cdns3_gadget_config() is called in cdns3_gadget_udc_start() and 
> cdns3_gadget_resume(). These settings seems to be needed during resume
> as well.

But this bit was never cleared in suspend so why do you need to set it again it in resume?

The commit log says that this bit must be kept set in low power states.

> 
>>>  	cdns3_configure_dmult(priv_dev, NULL);
>>>  
>>>  	cdns3_gadget_pullup(&priv_dev->gadget, 1);
>>> @@ -2378,6 +2381,7 @@ static int cdns3_gadget_udc_stop(struct usb_gadget *gadget)
>>>  
>>>  	/* disable interrupt for device */
>>>  	writel(0, &priv_dev->regs->usb_ien);
>>> +	writel(0, &priv_dev->regs->usb_pwr);
>>>  	writel(USB_CONF_DEVDS, &priv_dev->regs->usb_conf);
>>>  
>>>  	return ret;
>>>
>>> base-commit: a25dcda452bf6a6de72764a8d990d72e5def643d
>>

-- 
cheers,
-roger