[PATCH] usb: cdns3: use VBUS Valid to determine role for dr_mode OTG

[Marek Vasut]

On 2/4/26 1:12 PM, Siddharth Vadapalli wrote:
> The cdns3_bind() function is responsible for identifying the appropriate
> driver to bind to the USB Controller's device-tree node. If the device-tree
> node has the 'dr_mode' property set to 'otg', the existing approach fails
> to bind a driver, leading to loss of functionality.
> 
> To address this, use the VBUS Valid field of the OTG Status register to
> determine the role as follows:
> - If VBUS Valid field is set, it indicates that a USB Host is supplying
>    power and the Controller should assume the Peripheral role.
> - If VBUS Valid field is clear, it indicates the absence of a USB Host and
>    the Controller should assume the Host role.
> 
> Additionally, when 'dr_mode' happens to be 'otg' and the STRAP settings
> are not specified, use VBUS Valid to determine the role in cdns3_drd_init()
> and assign it to cdns->dr_mode.
> 
> Signed-off-by: Siddharth Vadapalli <s-vadapalli at ti.com>
> ---
> 
> Hello,
> 
> This patch is based on commit
> a8d982e1f17 x86: cpu: Fix crash on FTRACE enabled builds
> of the master branch of U-Boot.
> 
> Patch has been tested in the context of USB DFU boot on the J784S4 SoC
> with a Cadence USB 3.0 Controller. Since the Linux device-tree for the
> J784S4-EVM specifies the 'dr_mode' as OTG, due to reuse of Linux
> device-tree by U-Boot, the 'dr_mode' of 'otg' causes USB DFU Boot to fail.
> While one approach to fix it is to update 'dr_mode' to 'peripheral' in
> the 'k3-j784s4-u-boot.dtsi' file as a HACK, it doesn't scale to other
> SoCs and all of their 'u-boot.dtsi' files will have to be udpated as well.
> While I am providing Texas Instruments SoCs as an example, I presume that
> SoCs from other vendors are also affected by the 'dr_mode' being 'otg'.
> This patch addresses the issue by using the VBUS Valid bit of the OTG
> status register to override 'dr_mode' from 'otg' to a deterministic role
> to enable functionality.
> 
> The USB DFU Boot Logs for the R5 SPL stage on J784S4 SoC with the current
> U-Boot master as of commit
> a8d982e1f17 x86: cpu: Fix crash on FTRACE enabled builds
> are:
> https://gist.github.com/Siddharth-Vadapalli-at-TI/b910f326b6c9fad760190bd299ae3ff3
> and the logs indicate that USB DFU Boot fails. The failure is specifically
> due to 'dr_mode' being 'otg' and the cdns3_bind() function failing to bind
> the device-tree node to the peripheral driver required for DFU Boot.
> 
> The USB DFU Boot Logs for the R5 SPL stage with just this patch applied
> while leaving 'dr_mode' at its existing value of 'otg' are:
> https://gist.github.com/Siddharth-Vadapalli-at-TI/033b9772b6ab105b96806adf890848fe
> 
> Regards,
> Siddharth.
> 
>   drivers/usb/cdns3/core.c | 53 ++++++++++++++++++++++++++++++++++++++++
>   drivers/usb/cdns3/drd.c  | 11 +++++++++
>   2 files changed, 64 insertions(+)
> 
> diff --git a/drivers/usb/cdns3/core.c b/drivers/usb/cdns3/core.c
> index 4434dc15bec..b7be5c48fc9 100644
> --- a/drivers/usb/cdns3/core.c
> +++ b/drivers/usb/cdns3/core.c
> @@ -392,6 +392,55 @@ static const struct udevice_id cdns3_ids[] = {
>   	{ },
>   };
>   
> +/*
> + * The VBUS Valid Bit in the OTG Status register can be used to determine
> + * the role. When VBUS Valid is set, it indicates that a USB Host is supplying
> + * power, so the Controller should assume the PERIPHERAL role. If it isn't set,
> + * it indicates the absence of a USB Host, so the Controller should assume the
> + * HOST role. If the OTG Status register is inaccessible, return OTG role.
> + */
> +static enum usb_dr_mode cdns3_get_otg_mode(ofnode node)
> +{
> +	struct cdns3 cdns, *cdnsp;
> +	void __iomem *otg_regs;
> +	fdt_addr_t otg_addr;
> +	int otg_reg_index;
> +	int vbus;
> +
> +	otg_reg_index = ofnode_stringlist_search(node, "reg-names", "otg");
> +	if (otg_reg_index < 0)
> +		return USB_DR_MODE_OTG;
This is wrong, the function should return error and possibly mode via 
function parameter , do not conflate return value and mode please .