riscv_read_by_any_size() is redundant

[en-sc]

riscv_read_by_any_size() is used to try all available sizes when reading memory:

riscv-openocd/src/target/riscv/riscv.c

Lines 1392 to 1397 in eb9ba21

	/**
	* Read one memory item using any memory access size that will work.
	* Read larger section of memory and pick out the required portion, if needed.
	* */
	int riscv_read_by_any_size(struct target *target, target_addr_t address, uint32_t size, uint8_t *buffer)
	{

riscv_read_by_any_size() is currently used in riscv_semihosting() and in riscv_add_breakpoint() to read instructions.

There is also target_read_buffer(). It provides the same interface.
Seems like riscv_read_by_any_size() should be the implementation of target_read_buffer() (currently target_read_buffer_default() is used).

[JanMatCodasip]

Actually, the functions riscv_read_by_any_size() and target_read_buffer_default() work differently:

• riscv_read_by_any_size() tries to read certain amount of data from memory, and will try to use various access sizes until one of them succeeds. This function was introduced for architectures that do not support all access sizes when accessing special areas of memory that can hold program instructions (namely ICCM memory in VeeR EH1).
• target_read_buffer_default() will read certain amount of bytes using the largest transfer size possible in order to improve performance. It will not fall back to a different access size if the attempted access size is not supported - it will end with an error immediately.

[en-sc]

This function was introduced for architectures that do not support all access sizes when accessing special areas of memory that can hold program instructions

But the issue is target_read_buffer/target_write_buffer seems to be the functions intended to be used to access instruction memory.
This is evident from:

• The comment in target.h
  

  riscv-openocd/src/target/target.h

  Lines 635 to 641 in eb9ba21

  	/*
  	* Write to target memory using the virtual address.
  	*
  	* Note that this fn is used to implement software breakpoints. Targets
  	* can implement support for software breakpoints to memory marked as read
  	* only by making this fn write to ram even if it is read only(MMU or
  	* MPUs).

• The use in load_image handler:
  

  riscv-openocd/src/target/target.c

  Lines 3658 to 3659 in 2210897

  	retval = target_write_buffer(target,
  	image.sections[i].base_address + offset, length, buffer + offset);

Moreover, they are used throughout riscv.c for exactly that purpose:

• In riscv_checksum_memory():
  

  riscv-openocd/src/target/riscv/riscv.c

  Lines 3804 to 3805 in 2210897

  	retval = target_write_buffer(target, crc_algorithm->address, crc_code_size,
  	crc_code);

• In riscv_hit_watchpoint():
  

  riscv-openocd/src/target/riscv/riscv.c

  Line 2367 in 2210897

  if (target_read_buffer(target, dpc, length, buffer) != ERROR_OK) {

Finally, I don't get why the function can't do both: try multiple access sizes to be able to read any memory and try the largest size first to achieve the best possible performance.

[en-sc]

Somewhat related to #1184.