linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Refine the logic for resizing Tx FIFOs

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Message-ID: <b2ffd1ec-2168-4e58-8aee-b43f1231d4ac@quicinc.com>
Date: Thu, 5 Sep 2024 13:57:11 +0530
From: AKASH KUMAR <quic_akakum@...cinc.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jing Leng
	<jleng@...arella.com>, Felipe Balbi <balbi@...nel.org>,
        Jack Pham
	<quic_jackp@...cinc.com>,
        "kernel@...cinc.com" <kernel@...cinc.com>,
        "Wesley
 Cheng" <quic_wcheng@...cinc.com>,
        Laurent Pinchart
	<laurent.pinchart@...asonboard.com>,
        Daniel Scally
	<dan.scally@...asonboard.com>,
        Vijayavardhan Vennapusa
	<quic_vvreddy@...cinc.com>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Refine the logic for resizing Tx
 FIFOs

Hi Thinh,

On 9/5/2024 3:36 AM, Thinh Nguyen wrote:
> On Wed, Sep 04, 2024, AKASH KUMAR wrote:
>> Hi Thinh,
>>
>> On 9/4/2024 3:41 AM, Thinh Nguyen wrote:
>>> On Tue, Sep 03, 2024, Akash Kumar wrote:
>>>> The current logic is rigid, setting num_fifos to fixed values:
>>>>
>>>> 3 for any maxburst greater than 1.
>>>> tx_fifo_resize_max_num for maxburst greater than 6.
>>>> Additionally, it did not differentiate much between bulk and
>>>> isochronous transfers, applying similar logic to both.
>>>>
>>>> The new logic is more dynamic and tailored to the specific needs of
>>>> bulk and isochronous transfers:
>>>>
>>>> Bulk Transfers: Ensures that num_fifos is optimized by considering
>>>> both the maxburst value and the maximum allowed number of FIFOs.
>>>>
>>>> Isochronous Transfers: Ensures that num_fifos is sufficient by
>>>> considering the maxburst value and the maximum packet multiplier.
>>>>
>>>> This change aims to optimize the allocation of Tx FIFOs for both bulk
>>>> and isochronous endpoints, potentially improving data transfer
>>>> efficiency and overall performance.
>>>> It also enhances support for all use cases, which can be tweaked
>>>> with DT parameters and the endpoint’s maxburst and maxpacket.
>>>>
>>>> Signed-off-by: Akash Kumar <quic_akakum@...cinc.com>
>>>> ---
>>>> Changes for v2:
>>>> Redefine logic for resizing tx fifos.
>>>>
>>>> Changes for v1:
>>>> Added additional condition to allocate tx fifo for hs isoc eps,
>>>> keeping the other resize logic same.
>>>> ---
>>>>    drivers/usb/dwc3/gadget.c | 15 ++++++---------
>>>>    1 file changed, 6 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>> index 89fc690fdf34..49809a931104 100644
>>>> --- a/drivers/usb/dwc3/gadget.c
>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>> @@ -778,15 +778,12 @@ static int dwc3_gadget_resize_tx_fifos(struct dwc3_ep *dep)
>>>>    	ram1_depth = DWC3_RAM1_DEPTH(dwc->hwparams.hwparams7);
>>>> -	if ((dep->endpoint.maxburst > 1 &&
>>>> -	     usb_endpoint_xfer_bulk(dep->endpoint.desc)) ||
>>>> -	    usb_endpoint_xfer_isoc(dep->endpoint.desc))
>>>> -		num_fifos = 3;
>>>> -
>>>> -	if (dep->endpoint.maxburst > 6 &&
>>>> -	    (usb_endpoint_xfer_bulk(dep->endpoint.desc) ||
>>>> -	     usb_endpoint_xfer_isoc(dep->endpoint.desc)) && DWC3_IP_IS(DWC31))
>>>> -		num_fifos = dwc->tx_fifo_resize_max_num;
>>>> +	if (usb_endpoint_xfer_bulk(dep->endpoint.desc))
>>>> +		num_fifos = min_t(unsigned int, dep->endpoint.maxburst + 1,
>>>> +				  dwc->tx_fifo_resize_max_num);
>>>> +	if (usb_endpoint_xfer_isoc(dep->endpoint.desc))
>>>> +		num_fifos = max_t(unsigned int, dep->endpoint.maxburst,
>>>> +				  usb_endpoint_maxp_mult(dep->endpoint.desc));
>>> No. Don't mix usb_endpoint_maxp_mult with maxburst like this. Check base
>>> on operating speed. Also, now you're ignoring tx_fifo_resize_max_num for
>>> isoc.
>> Sure will add separate check based on speed.
>>
>> We have to support three versions of CAM support through same dt and image
>> SS/SS+ capable cam which needs 10k fifo
>> HS cams which needs 3K
>> multi UVC cams which needs 1k and 2k fifo
>>
>> Putting any dependency with tx_fifo_resize_max_num, we can't achieve 1k and
>> 10K,
> That doesn't make sense. The tx_fifo_resize_max_num is a configurable
> constraint through devicetree property. How can it not work?
i have tested and i don't have any problem in adding constraint with HS 
but for SS
i need to set fifo size of 1K for 1 cam and 10k for other.
if i add any boundary with tx_fifo_resize_max_num (either max or min ) 
one of tx fifo size
either 1k or 10K i won't be able to set. So i request you allow to for 
 >=SS , to decide fifo
size based on maxburst only. i will be pusing patchset3 with that. 
please approve consideration this.
>> it has to be decided by maxbursts itself which user can configure.
>> All uvc gadget applications supports configurable maxburst which they use
>> while opening,
>> so it should be better for isoc eps to decide fifo based on maxbursts.
>>
> We should not just look at maxburst. It's only applicable to usb3
> speeds. How the function driver configures maxp_mult* vs maxbursts is
> independent. So let's keep the check separate base on speed for isoc.
>
> Thanks,
> Thinh
>
> [*] Let's refer the mouthful "additional transaction opportunities" as
> maxp_mult.

yes of course i will add separate check for maxp_mult in patchset3 for 
<=HS speed devices.

Thanks,
Akash