On 5/15/19 2:34 AM, Arnd Bergmann wrote: >> +static void gsi_trans_tre_fill(struct gsi_tre *dest_tre, dma_addr_t addr, >> + u32 len, bool last_tre, bool bei, >> + enum ipa_cmd_opcode opcode) >> +{ >> + struct gsi_tre tre; >> + >> + tre.addr = cpu_to_le64(addr); >> + tre.len_opcode = gsi_tre_len_opcode(opcode, len); >> + tre.reserved = 0; >> + tre.flags = gsi_tre_flags(last_tre, bei, opcode); >> + >> + *dest_tre = tre; /* Write TRE as a single (16-byte) unit */ >> +} > Have you checked that the atomic write is actually what happens here, > but looking at the compiler output? You might need to add a 'volatile' > qualifier to the dest_tre argument so the temporary structure doesn't > get optimized away here.
Currently, the assignment *does* become a "stp" instruction. But I don't know that we can *force* the compiler to write it as a pair of registers, so I'll soften the comment with "Attempt to write" or something similar. To my knowledge, adding a volatile qualifier only prevents the compiler from performing funny optimizations, but that has no effect on whether the 128-bit assignment is made as a single unit. Do you know otherwise? -Alex