[U-Boot] dfu: dfu and UBI Volumes

[Pantelis Antoniou]

Hi 
On May 28, 2013, at 7:43 PM, Benoît Thébaudeau wrote:

> Hi Pantelis,
> 
> On Tuesday, May 28, 2013 6:43:06 PM, Pantelis Antoniou wrote:
>> Hi Benoît
>> 
>> On May 28, 2013, at 7:31 PM, Benoît Thébaudeau wrote:
>> 
>>> Dear Pantelis Antoniou,
>>> 
>>> On Tuesday, May 28, 2013 5:05:12 PM, Pantelis Antoniou wrote:
>>>> Hi Tom,
>>>> 
>>>> On May 28, 2013, at 6:01 PM, Tom Rini wrote:
>>>> 
>>>>> On Tue, May 28, 2013 at 07:50:46AM +0200, Wolfgang Denk wrote:
>>>>>> Dear Tom,
>>>>>> 
>>>>>> In message <20130527233735.GZ17119 at bill-the-cat> you wrote:
>>>>>>> 
>>>>>>>> Where exactly is this 8 MB limit coming into play?
>>>>>>> 
>>>>>>> In buffering the data.  We cannot write a chunk of a file to a
>>>>>>> filesystem and then append to it, we don't have the API today.
>>>>>> 
>>>>>> Sorry, I still don't get it. Assuming I have a GiB of RAM, why can I
>>>>>> not load a 256 MiB file to RAM, and then write it to a file system?
>>>>>> 
>>>>>> I have definitely dealt with images and files bigger than 8 MiB in
>>>>>> thepast, so I really don't see where any buffer problem could be.
>>>>> 
>>>>> I thought I might not have been clear about where this limit comes from,
>>>>> after I sent the email.  The problem we have, and this is only for
>>>>> writing to a filesystem (_not_ writing of a filesystem) is that we do
>>>>> not have the API for appending to files, only create/overwrite.  So we
>>>>> must read the whole file into memory, and then write it out.  The DFU
>>>>> protocol doesn't have (I would swear anyhow) a part where it says "I'm
>>>>> about to send you a blob of X bytes", so we cannot know at the start how
>>>>> much data is coming our way.
>>>>> 
>>>>> Today we "solve" this with a statically defined
>>>>> CONFIG_SYS_DFU_MAX_FILE_SIZE.  Looking at things again, I think this is
>>>>> buggy right now in that we need to also whack DFU_DATA_BUF_SIZE to also
>>>>> be that same value.  Going forward, we may be able to switch this to
>>>>> (and both of these are off the top of my head) a getenv to see how much
>>>>> space to malloc, or just making it a malloc and adding some compile-time
>>>>> check to ensure that the malloc area is at least as big as
>>>>> CONFIG_SYS_DFU_MAX_FILE_SIZE.
>>>>> 
>>>> 
>>>> Correct, the DFU protocol doesn't have a method to inform you before hand
>>>> about the size of the transfer about to happen.
>>>> 
>>>> The only possible solution I see at this point is to have an environment
>>>> variable, i.e. dfubuf that controls the size of the buffer.
>>>> 
>>>> Upon start of a dfu transfer we can allocate the buffer, and do our
>>>> thing.
>>> 
>>> I don't know the details of the DFU implementation in U-Boot, but the
>>> specification leaves the choice between programming the firmware on-the-fly
>>> during the download, and later during the manifestation phase (or a mix of
>>> both). Hence, there is not need for a global firmware buffer if U-Boot goes
>>> for
>>> the on-the-fly programming strategy. The only buffer constraint would be
>>> wTransferSize (chosen by U-Boot for the control endpoint) in that case. See
>>> "7. Manifestation Phase" on page 26 here:
>>> http://www.usb.org/developers/devclass_docs/DFU_1.1.pdf
>>> 
>> 
>> The problem is not DFU TBH, it's that since we don't have an option to append
>> to a file, we have to have the whole file transferred in RAM and written in
>> one go. The raw medium dfu methods in u-boot don't have a problem.
>> 
>>> Of course this can't yet apply to writing files on file systems since the
>>> current API in U-Boot misses the append feature, but this could be applied
>>> to
>>> program raw memory partitions, including UBI images.
>>> 
>> 
>> It already happens for raw memory partitions, it's the UBI images being
>> discussed.
> 
> But what does appending to a file has to do with programming a UBI image, which
> is a memory partition containing a whole file system? This is what I don't get
> in this discussion. Is it because of a restriction of the DFU API in U-Boot?
> 

Don't expect a discussion on a mailing list to stay on topic for long :)
We sort of drifted from UBI to the fixed sized buffer.

> Best regards,
> Benoît

Regards

-- Pantelis