linux-kernel - Re: [PATCH v5 4/5] xhci: mediatek: support MTK xHCI host controller

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Date:	Wed, 19 Aug 2015 19:21:13 +0800
From:	chunfeng yun <chunfeng.yun@...iatek.com>
To:	Mathias Nyman <mathias.nyman@...ux.intel.com>
CC:	Mathias Nyman <mathias.nyman@...el.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	"Matthias Brugger" <matthias.bgg@...il.com>,
	Felipe Balbi <balbi@...com>,
	"Sascha Hauer" <s.hauer@...gutronix.de>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	"Roger Quadros" <rogerq@...com>, <linux-usb@...r.kernel.org>,
	<linux-mediatek@...ts.infradead.org>,
	John Crispin <blogic@...nwrt.org>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH v5 4/5] xhci: mediatek: support MTK xHCI host controller

Hi
On Mon, 2015-08-17 at 18:07 +0300, Mathias Nyman wrote:
> Hi
> 
> On 07.08.2015 15:30, Chunfeng Yun wrote:
> > MTK xhci host controller defines some extra SW scheduling
> > parameters for HW to minimize the scheduling effort for
> > synchronous and interrupt endpoints. The parameters are
> > put into reseved DWs of slot context and endpoint context
> >
> >
> 
> ...
> 
> > + * The TD size is the number of max packet sized packets remaining in the TD
> > + * (including this TRB), right shifted by 10.
> > + * It must fit in bits 21:17, so it can't be bigger than 31.
> > + */
> > +u32 xhci_mtk_td_remainder_quirk(unsigned int td_running_total,
> > +	unsigned trb_buffer_length, struct urb *urb)
> > +{
> > +	u32 max = 31;
> > +	int remainder, td_packet_count, packet_transferred;
> > +	unsigned int td_transfer_size = urb->transfer_buffer_length;
> > +	unsigned int maxp;
> > +
> > +	maxp = GET_MAX_PACKET(usb_endpoint_maxp(&urb->ep->desc));
> > +
> > +	/* 0 for the last TRB */
> > +	if (td_running_total + trb_buffer_length == td_transfer_size)
> > +		return 0;
> > +
> > +	packet_transferred = td_running_total / maxp;
> > +	td_packet_count = DIV_ROUND_UP(td_transfer_size, maxp);
> > +	remainder = td_packet_count - packet_transferred;
> > +
> > +	if (remainder > max)
> > +		return max << 17;
> > +	else
> > +		return remainder << 17;
> > +}
> 
> I started looking at this xhci_mtk_td_remainder() function, one
> of the places this patch touches the existing xhci code.
> 
> The remainder functions in xhci are already bit too messy, and
> adding one more function which does almost the same thing makes
> it even messier.
> 
> For example queuing a bulk transfer will end up like this:
> 
> >   		/* Set the TRB length, TD size, and interrupter fields. */
> >   		if (xhci->hci_version < 0x100) {
> > -			remainder = xhci_td_remainder(
> > +			if (xhci->quirks & XHCI_MTK_HOST) {
> > +				remainder = xhci_mtk_td_remainder_quirk(
> > +					running_total, trb_buff_len, urb);
> > +			} else {
> > +				remainder = xhci_td_remainder(
> >   					urb->transfer_buffer_length -
> >   					running_total);
> > +			}
> >   		} else {
> >   			remainder = xhci_v1_0_td_remainder(running_total,
> >   					trb_buff_len, total_packet_count, urb,
> 
> and similar for isoc and control transfers.
> 
> I'll see if I can simplify the existing remainder calculations into one function, then it should
> be enough to just add something like this into it:
> 
> if (xhci->quirks & XHCI_MTK_HOST)
> 	trb_buff_len = 0;
>   	
> This way we can skip all the extra hassle that comes with a new exported quirk function
> 
> Is the Mediatek xhci really a xHCI 0.96 or older controller? (hci_version < 0x100)
> Not a xHCI 1.0 or 1.1 ?
> 
It is xHCI 0.96, but add some feature of xHCI 1.0

Thanks a lot

> -Mathias


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