Re: [PATCH] crypto: crc32: make crc32 available in PBL

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 29.08.23 12:55, Johannes Zink wrote:
> On 8/29/23 12:45, Ahmad Fatoum wrote:
>>>> +lwl-$(CONFIG_CRC32_EARLY)        += crc32.o
>>>
>>> pbl-obj- is the correct prefix. lwl- means pbl- if we have PBL
>>> support at all and obj- otherwise (for legacy systems without PBL),
>>> while pbl-obj- is equivalent to duplicating the line once with pbl-
>>> and once with obj-
>>
>> s/pbl-obj-/obj-pbl-/ :)

Sorry, had a small brain fart here.

You didn't remove the original obj-,
so now lwl- either expands to and extra obj- or to pbl-.

obj-pbl- makes sense when you use the same symbol for both PBL and
barebox proper, but as you're introducing a new symbol, you can
leave it as lwl- or make it pbl- for explicitness.

> ack, gonna fix this for v2.
> 
>>>
>>>>   obj-$(CONFIG_DIGEST_SHA384_GENERIC)    += sha4.o
>>>>   obj-$(CONFIG_DIGEST_SHA512_GENERIC)    += sha4.o
>>>>   obj-y    += memneq.o
>>>> diff --git a/crypto/crc32.c b/crypto/crc32.c
>>>> index 95cb2212db2b..284d39351682 100644
>>>> --- a/crypto/crc32.c
>>>> +++ b/crypto/crc32.c
>>>> @@ -22,7 +22,7 @@
>>>>   #define STATIC static inline
>>>>   #endif
>>>>   -#ifdef CONFIG_DYNAMIC_CRC_TABLE
>>>> +#if defined(CONFIG_DYNAMIC_CRC_TABLE) && !defined(__PBL__)
>>>
>>> You could also replace the dynamic allocation with a static array initialized
>>> to zero. That way you can have a dynamic crc table even in PBL without affecting
>>> image size as the BSS is not part of the image.
> 
> ack. Is this ok?
> 
> #ifdef __PBL__
>   static uint32_t _crc_table_memory[sizeof(uint32_t) * 256] = { 0 };

The array is 256 elements, not 1024 elements. Explicit intialization
is unnecessary.

> #endif
> 
> static void *alloc_crc_table() {
> #ifdef __PBL__
>     return _crc_table_memory;
> #else
>     return xmalloc(sizeof(uint32_t) * 256);
> #endif
> }
> 
> If so, I can change it for v2.

My idea was to drop the allocation altogether by using BSS.
If you do this, you should not need any __PBL__ checking at all.

Either you have CONFIG_DYNAMIC_CRC_TABLE and the table is dynamically
filled in bss on first access or you have CONFIG_DYNAMIC_CRC_TABLE=n
and the table is already there and need not be allocated.

On a second thought, I am not sure if we want a table at all in PBL.
Do you do a lot of CRC32 computation? Maybe we should just not use
a table at all in PBL and just calculate a single crc32?
That's what Sascha did here:

2d13b856604b ("crc: Add PBL variant for crc_itu_t()")

Let me know what you think.

Cheers,
Ahmad

> 
> Best regards
> Johannes
> 
> 
>>>
>>>>     static uint32_t *crc_table;
>>>>   @@ -145,7 +145,7 @@ STATIC uint32_t crc32(uint32_t crc, const void *_buf, unsigned int len)
>>>>   {
>>>>       const unsigned char *buf = _buf;
>>>>   -#ifdef CONFIG_DYNAMIC_CRC_TABLE
>>>> +#if defined(CONFIG_DYNAMIC_CRC_TABLE) && !defined(__PBL__)
>>>>       if (!crc_table)
>>>>           make_crc_table();
>>>>   #endif
>>>> @@ -171,7 +171,7 @@ STATIC uint32_t crc32_no_comp(uint32_t crc, const void *_buf, unsigned int len)
>>>>   {
>>>>      const unsigned char *buf = _buf;
>>>>   -#ifdef CONFIG_DYNAMIC_CRC_TABLE
>>>> +#if defined(CONFIG_DYNAMIC_CRC_TABLE) && !defined(__PBL__)
>>>>       if (!crc_table)
>>>>           make_crc_table();
>>>>   #endif
>>>>
>>>> ---
>>>> base-commit: bef38b18eeb5d2f1fac334fb8b831e47261e099c
>>>> change-id: 20230829-crc32_in_pbl-4d824629d4e2
>>>>
>>>> Best regards,
>>>
>>
> 

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