Re: [PATCH v12 3/6] usb: dwc3: Resize TX FIFOs to meet EP bursting requirements

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jul 02, 2021 at 02:37:32AM -0700, Wesley Cheng wrote:
> Some devices have USB compositions which may require multiple endpoints
> that support EP bursting.  HW defined TX FIFO sizes may not always be
> sufficient for these compositions.  By utilizing flexible TX FIFO
> allocation, this allows for endpoints to request the required FIFO depth to
> achieve higher bandwidth.  With some higher bMaxBurst configurations, using
> a larger TX FIFO size results in better TX throughput.
> 
> By introducing the check_config() callback, the resizing logic can fetch
> the maximum number of endpoints used in the USB composition (can contain
> multiple configurations), which helps ensure that the resizing logic can
> fulfill the configuration(s), or return an error to the gadget layer
> otherwise during bind time.
> 
> Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
> ---
>  drivers/usb/dwc3/core.c   |   9 ++
>  drivers/usb/dwc3/core.h   |  15 ++++
>  drivers/usb/dwc3/ep0.c    |   2 +
>  drivers/usb/dwc3/gadget.c | 221 ++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 247 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index e0a8e79..a7bcdb9d 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1267,6 +1267,7 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>  	u8			rx_max_burst_prd;
>  	u8			tx_thr_num_pkt_prd;
>  	u8			tx_max_burst_prd;
> +	u8			tx_fifo_resize_max_num;
>  	const char		*usb_psy_name;
>  	int			ret;
>  
> @@ -1282,6 +1283,8 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>  	 */
>  	hird_threshold = 12;
>  
> +	tx_fifo_resize_max_num = 6;
> +

No comment as to why 6 was picked, like the other defaults in this
function?

Why was 6 picked?


>  	dwc->maximum_speed = usb_get_maximum_speed(dev);
>  	dwc->max_ssp_rate = usb_get_maximum_ssp_rate(dev);
>  	dwc->dr_mode = usb_get_dr_mode(dev);
> @@ -1325,6 +1328,10 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>  				&tx_thr_num_pkt_prd);
>  	device_property_read_u8(dev, "snps,tx-max-burst-prd",
>  				&tx_max_burst_prd);
> +	dwc->do_fifo_resize = device_property_read_bool(dev,
> +							"tx-fifo-resize");
> +	device_property_read_u8(dev, "tx-fifo-max-num",
> +				&tx_fifo_resize_max_num);

So you overwrite the "max" with whatever is given to you?  What if
tx-fifo-resize is not enabled?

thanks,

greg k-h