[U-Boot] [U-Boot, v3, 1/2] fs: fat: dynamically allocate memory for temporary buffer

[Marek Vasut]

On 2/21/19 9:55 AM, Alexander Graf wrote:
> 
> 
> On 21.02.19 09:49, Marek Vasut wrote:
>> On 2/21/19 9:44 AM, Alexander Graf wrote:
>>>
>>>
>>> On 21.02.19 09:41, Marek Vasut wrote:
>>>> On 2/21/19 9:40 AM, Chee, Tien Fong wrote:
>>>>> On Thu, 2019-02-21 at 09:29 +0100, Alexander Graf wrote:
>>>>>>
>>>>>> On 21.02.19 09:23, Chee, Tien Fong wrote:
>>>>>>>
>>>>>>> On Thu, 2019-02-21 at 08:45 +0100, Michal Simek wrote:
>>>>>>>>
>>>>>>>> Hi Tom,
>>>>>>>>
>>>>>>>> On 20. 02. 19 2:58, Tom Rini wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Mon, Feb 11, 2019 at 02:56:19PM +0800, tien.fong.chee at intel.
>>>>>>>>> com
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> From: Tien Fong Chee <tien.fong.chee at intel.com>
>>>>>>>>>>
>>>>>>>>>> Drop the statically allocated get_contents_vfatname_block and
>>>>>>>>>> dynamically allocate a buffer only if required. This saves
>>>>>>>>>> 64KiB of memory.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Stefan Agner <stefan.ag... at toradex.com>
>>>>>>>>>> Signed-off-by: Tien Fong Chee <tien.fong.chee at intel.com>
>>>>>>>>> Applied to u-boot/master, thanks!
>>>>>>>> please remove this patch (better both of them because they were
>>>>>>>> in
>>>>>>>> series)
>>>>>>> I think patch 2/2 should be safe, because no memory size is
>>>>>>> changed.
>>>>>>> Basically, it just to release the allocated memory immediately when
>>>>>>> it's not required, so other can re-use it.
>>>>>>>
>>>>>>>>
>>>>>>>> because they are breaking at least ZynqMP SPL. It is also too
>>>>>>>> late in cycle to create random fix.
>>>>>>>>
>>>>>>>> You can't simply move 64KB from code to malloc without reflecting
>>>>>>>> this
>>>>>>>> by changing MALLOC space size.
>>>>>>>>
>>>>>>>> Other boards with SPL fat could be also affected by this if they
>>>>>>>> don't
>>>>>>>> allocate big malloc space.
>>>>>>> So, any suggestion to get the patch 1/2 accepted? inform all board
>>>>>>> maintainers to test it out?
>>>>>> You already received feedback that it does break ZynqMP, so the
>>>>>> current
>>>>>> approach won't work.
>>>>>>
>>>>>> How about you create a new kconfig option that allows you to say
>>>>>> whether
>>>>>> you want to use malloc or .bss for temporary data in the FAT driver.
>>>>>> You
>>>>>> can then have an _SPL_ version of that kconfig and check for it with
>>>>>> IS_ENABLED() which should automatically tell you the right answer
>>>>>> depending on whether you're in an SPL build or not.
>>>>>>
>>>>>> Then you can set the SPL version to default malloc and the non-SPL
>>>>>> version to default .bss.
>>>>> Marek and Tom rini,
>>>>>
>>>>> Are you guys okay with Alex's suggestion?
>>>>
>>>> I'm not a big fan of adding more and more ifdeffery.
>>>> Is there some other option ?
>>>
>>> Is RAM up already at this point? Maybe we could improve the SPL malloc
>>> mechanism to move allocations into DRAM once it's available.
>>
>> Well, the FAT buffers waste some 64kiB of bss, so we can use that area
>> for malloc instead, no ?
> 
> Yes, but that means you need to review every single board that uses FAT
> in SPL today and adjust its malloc region size.

That's quite likely ... I still think this patch is beneficial, it's
much better to dynamically allocate the cluster size than have this
64kiB chunk of BSS carved out.

-- 
Best regards,
Marek Vasut