[U-Boot] [PATCH] usb_storage: fix ehci driver max transfer size

[Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>]

Am 03.07.2012 20:10, schrieb Marek Vasut:
>> The commit 5dd95cf93dfffa1d19a1928990852aac9f55b9d9 'usb_storage:
>> Fix EHCI "out of buffer pointers" with CD-ROM' introduce a bug in
>> usb_storage as it wrongly assumes that every transfer can use 4k
>> per qt_buffer. This is wrong if the start address of the data
>> is not 4k aligned and leads to 'EHCI timed out on TD' messages
>> because of 'out of buffer pointers' in ehci_td_buffer function.
>>
>> Cc: Marek Vasut <marex@denx.de>
>> Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>
> Ok, first I have to admit I broke my promise to look into this ASAP, sorry about
> it :-(
No problem, as long as we get it into the next release. ;-)
>
> Just curious, but shouldn't it be ((4096 * 5) / dev_desc->blk_sz) - 1 ?
No, because the first blk need to be aligned with the 4096. In worst 
case the blk is at the end of the 4096 range. If we assume that the blk 
is aligned to blk_sz we can change it to ((4096 * 4) / dev_desc->blk_sz) 
+ 1. I skip the last blk (+ 1) because with 4096 aligned first blk we 
unaligned the next transfer and add extra short packages to each ehci 
transfer.

If we want to maximise the usage we need to calculate the max_xfer_blk 
depending on the start address of the first blk.

>> ---
>>   common/usb_storage.c |    6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/common/usb_storage.c b/common/usb_storage.c
>> index faad237..612a553 100644
>> --- a/common/usb_storage.c
>> +++ b/common/usb_storage.c
>> @@ -1416,10 +1416,10 @@ int usb_stor_get_info(struct usb_device *dev,
>> struct us_data *ss, USB_STOR_PRINTF("partype: %d\n", dev_desc->part_type);
>>
>>   	/*
>> -	 * The U-Boot EHCI driver cannot handle more than 4096 * 5 bytes in a
>> -	 * transfer without running itself out of qt_buffers.
>> +	 * The U-Boot EHCI driver cannot handle more than 4096 * 4 bytes in a
>> +	 * unaligned transfer without running itself out of qt_buffers.
>>   	 */
>> -	ss->max_xfer_blk = (4096 * 5) / dev_desc->blksz;
>> +	ss->max_xfer_blk = (4096 * 4) / dev_desc->blksz;
>>
>>   	init_part(dev_desc);
>