About XHCI_TD_PAGE_SIZE.

[Kohji Okuno]

From: Hans Petter Selasky <hps at selasky.org>
Subject: Re: About XHCI_TD_PAGE_SIZE.
Date: Sat, 20 Dec 2014 10:30:36 +0100

> On 12/17/14 05:42, Nidal Khalil wrote:
>> I agree. Thanks
>>
>> Nidal
>> On Dec 16, 2014 6:25 PM, "Kohji Okuno" <okuno.kohji at jp.panasonic.com> wrote:
>>
>>> Hi Hans,
>>>
>>> If we use PAGE_SIZE as USB_PAGE_SIZE, we should use PAGE_SIZE as
>>> XHCI_TD_PAGE_SIZE, too. I think.
>>>
>>> As you know, one TRB can use 1~64kB for the transfer length.
>>>
> 
> Hi,
> 
> We currently only check if 4K pages are supported by the hardware. If you
> change the value of XHCI_TD_PAGE_SIZE, you will also need to change the checks
> other places. You know that PAGE_SIZE is not a constant?
> 
> Do you have a complete patch?
> 
> --HPS
> 

Hi,

XHCI_TD_PAGE_SIZE is used at only 2-points.

1. use as XHCI_TD_PAYLOAD_MAX (XHCI_TD_PAGE_NBUF) in xhci.h
   We sholud change as the following, I think.
   
- #define XHCI_TD_PAGE_NBUF	17	/* units, room enough for 64Kbytes */
- #define XHCI_TD_PAGE_SIZE	4096	/* bytes */
- #define XHCI_TD_PAYLOAD_MAX	(XHCI_TD_PAGE_SIZE * (XHCI_TD_PAGE_NBUF - 1))
+ #define XHCI_TD_PAYLOAD_MAX	(64*1024)	/* bytes */	   
+ #define XHCI_TD_PAGE_SIZE	PAGE_SIZE	/* bytes */
+ /* units, room enough for 64Kbytes */
+ #define XHCI_TD_PAGE_NBUF	(XHCI_TD_PAYLOAD_MAX/XHCI_TD_PAGE_SIZE + 1)

2. use as the maximum length of TRB.
   If PAGE_SIZE is 8kB, buf_res.length may be 8kB.
   But, we can set 1B~64kB for length of TRB. This is the spcification
   of xHCI. So, we don't need change this point.
   
xhci.c
1807                                 /* check for maximum length */
1808                                 if (buf_res.length > XHCI_TD_PAGE_SIZE)
1809                                         buf_res.length = XHCI_TD_PAGE_SIZE;


Best regards,
 Kohji Okuno