Compile error if CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM set to 1

[wy-hh]

After PR #29232 merged, I get compile error , if I define CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM to 1 for our platform.

Here is my found, if there is something wrong, please let me know.

Defining CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM to 1 makes CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL to 0.
Then CHIP_SYSTEM_CONFIG_PACKETBUFFER_CAPACITY_MAX, not used for LwIP-based platform, is required in class PacketBuffer as below.

#if CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL
    static constexpr uint16_t kMaxSizeWithoutReserve = LWIP_MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE);
#else
    static constexpr uint16_t kMaxSizeWithoutReserve = CHIP_SYSTEM_CONFIG_PACKETBUFFER_CAPACITY_MAX;
#endif

[bzbarsky-apple]

Is kMaxSizeWithoutReserve not used with lwip? It sure seems to be used....

What is the right setting of kMaxSizeWithoutReserve when doing CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM?

[bzbarsky-apple]

@kpschoedel can you please take a look?

[kpschoedel]

Did you previously use #define CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE PBUF_RAM?
I think then, because of the error that #29208 called out, CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL was (incorrectly) set to 1, and this was never caught because there's no in-tree build using this configuration.

We would preserve the previous behaviour here by changing that line

#if CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL

to

#if CHIP_SYSTEM_CONFIG_USE_LWIP

and I don't immediately see any other unexpected consequences of #29208.

[wy-hh]

@kpschoedel Matter currently doesn't fully support PBUF_RAM with original LWIP code, so there is no platform enabled in public Matter repo and no auto build detects it.
We use #define CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE PBUF_RAM to only pass pbuf_type paramter to pbuf_alloc in PacketBufferHandle::New under our repo for some PBUF_RAM experimental developments.

I think changing to #if CHIP_SYSTEM_CONFIG_USE_LWIP works for our platform.