On 21.01.22 17:54, Kevin O'Connor wrote:
On Fri, Jan 21, 2022 at 05:41:17PM +0100, Alexander Graf wrote:
On 21.01.22 17:02, Kevin O'Connor wrote:
On Fri, Jan 21, 2022 at 03:28:33PM +0100, Alexander Graf wrote:
On 19.01.22 19:45, Kevin O'Connor wrote:
if ((ns->block_size * count) > (NVME_PAGE_SIZE * 2)) {
/* We need to describe more than 2 pages, rely on PRP List */prp2 = ns->prpl;
/* We need to describe more than 2 pages, build PRP List */u32 prpl_len = 0;u64 *prpl = (void*)ns->dma_buffer;At 15*8=120 bytes of data, do we even need to put the prpl into dma_buffer or can we just use the stack? Will the array be guaranteed 64bit aligned or would we need to add an attribute to it?
u64 prpl[NVME_MAX_PRPL_ENTRIES];Either way, I don't have strong feelings one way or another. It just seems more natural to keep the bounce buffer purely as bounce buffer :).
In general it's possible to DMA from the stack (eg, src/hw/ohci.c:ohci_send_pipe() ). However, SeaBIOS doesn't guarantee stack alignment so it would need to be done manually. Also, I'm not sure how tight the nvme request completion code is - if it returns early for some reason it could cause havoc (device dma into random memory).
Another option might be to make a single global prpl array, but that would consume the memory even if nvme isn't in use.
FWIW though, I don't see a harm in the single ( u64 *prpl = (void*)ns->dma_buffer ) line.
Fair, works for me. But then we probably want to also adjust MAX_PRPL_ENTRIES to match the full page we now have available, no?
I don't think a BIOS disk request can be over 64KiB so I don't think it matters. I got the impression the current checks are just "sanity checks". I don't see a harm in keeping the sanity check and that size is as good as any other as far as I know.
It's a bit of both: Sanity checks and code that potentially can be reused outside of the SeaBIOS context. So I would try as hard as possible to not make assumptions that we can only handle max 64kb I/O requests. Plus, if we really wanted to, we could even introduce a new SeaBIOS specific INT to do larger I/O requests.
I won't make a fuss if you want to keep it at 64kb max request size though :).
Alex
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