Re: [PATCH v9 4/5] xhci: mediatek: support MTK xHCI host controller

[chunfeng yun <chunfeng.yun@mediatek.com>]

Hi,
On Thu, 2015-10-08 at 16:05 +0300, Mathias Nyman wrote:
> On 08.10.2015 15:28, Daniel Thompson wrote:
> > On 08/10/15 13:05, chunfeng yun wrote:
> >> Hi,
> >> On Thu, 2015-10-01 at 12:44 +0100, Daniel Thompson wrote:
> >>> On 29/09/15 04:01, Chunfeng Yun wrote:
> >>>> There some vendor quirks for MTK xhci host controller:
> >>>> 1. It 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.
> >>>> 2. Its IMODI unit for Interrupter Moderation register is
> >>>>     8 times as much as that defined in xHCI spec.
> >>>> 3. Its TDS in  Normal TRB defines a number of packets that
> >>>>     remains to be transferred for a TD after processing all
> >>>>     Max packets in all previous TRBs.
> >>>>
> >>>> Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> >>>
> >>> I've done some basic soak tests, both with a directly attached USB3 HDD
> >>> and, given the extra code to manage isochronous xfer, also with a hub,
> >>> disc and two audio interfaces.
> >>>
> >>> Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
> >>>
> >>>
> >>>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> >>>> index 57f40a1..243f696 100644
> >>>> --- a/drivers/usb/host/xhci-ring.c
> >>>> +++ b/drivers/usb/host/xhci-ring.c
> >>>> @@ -68,6 +68,7 @@
> >>>>    #include <linux/slab.h>
> >>>>    #include "xhci.h"
> >>>>    #include "xhci-trace.h"
> >>>> +#include "xhci-mtk.h"
> >>>>
> >>>>    /*
> >>>>     * Returns zero if the TRB isn't in this segment, otherwise it returns the DMA
> >>>> @@ -3044,18 +3045,27 @@ static u32 xhci_td_remainder(struct xhci_hcd *xhci, int transferred,
> >>>>                      struct urb *urb, unsigned int num_trbs_left)
> >>>>    {
> >>>>        u32 maxp, total_packet_count;
> >>>> +    u32 skip_current_trb = 0;
> >>>
> >>> A bit of a nitpick but why do we need skip_current_trb? Testing
> >>> (xhci->quirks & XHCI_MTK_HOST) twice would make what the code does, and
> >>> why, more obvious.
> >>>
> >> I am not sure which way it is better, so add variable of
> >> skip_current_trb to reduce test times.
> >
> > I can't imagine either approach impacts performance. However introducing skip_current_trb makes the flow of the branches harder to follow.
> >
> > The first branch was a version check and can remain so; we only need to do something special with the quirks because the MTK controller is 0.97 but with a few bits added:
> >
> >      /* MTK xHCI is mostly 0.97 but contains some features from 1.0 */
> >      if (xhci->hci_version < 0x100 && !(xhci->quirks & XHCI_MTK_HOST))
> >          return ...
> >
> > Setting trb_buff_len to zero is accommodating a quirk and this is clearer when we have:
> >
> >      /* for MTK xHCI, TD size doesn't include this TRB */
> >      if (xhci->quirks & XHCI_MTK_HOST)
> >          trb_buff_len = 0;
> 
> Both will work, but I'd prefer this solution as well.
> 
Thanks for your suggestion as well

> -Mathias
>