Re: [PATCH 2/2] i3c/master: add the mipi-i3c-hci driver

Boris Brezillon
2020-08-20T16:56:52Z

On Thu, 20 Aug 2020 12:34:13 -0400 (EDT)
Nicolas Pitre <nico@fluxnic.net> wrote:

> On Thu, 20 Aug 2020, Miquel Raynal wrote:

> > > +
> > > +#ccflags-y := -DDEBUG
> >
> > Probably a leftover?
>
> Well, I left it there intentionally as the code is still actively being
> developed, so full debugging can quickly be reactivated by anyone.
> I can remove it if deemed too distracting.

How about using dynamic printk instead? I'm pretty sure you don't need
to debug I3C stuff early enough to warrant usage of DDEBUG.

>
> > [...]
> >
> > > +#define CMD_C1_DATA_LENGTH(v) FIELD_PREP(W1_MASK(63, 48), v)
> > > +#define CMD_C1_OFFSET(v) FIELD_PREP(W1_MASK(47, 32), v)
> > > +#define CMD_C0_TOC W0_BIT_(31)
> > > +#define CMD_C0_ROC W0_BIT_(30)
> > > +#define CMD_C0_RNW W0_BIT_(29)
> > > +#define CMD_C0_MODE(v) FIELD_PREP(W0_MASK(28, 26), v)
> > > +#define CMD_C0_16_BIT_SUBOFFSET W0_bit(25)
> > > +#define CMD_C0_FIRST_PHASE_MODE W0_BIT_(24)
> > > +#define CMD_C0_DATA_LENGTH_POSITION(v) FIELD_PREP(W0_MASK(23, 22), v)
> > > +#define CMD_C0_DEV_INDEX(v) FIELD_PREP(W0_MASK(20, 16), v)
> > > +#define CMD_C0_CP W0_BIT_(15)
> > > +#define CMD_C0_CMD(v) FIELD_PREP(W0_MASK(14, 7), v)
> > > +#define CMD_C0_TID(v) FIELD_PREP(W0_MASK(6, 3), v)
> > > +
> > > +/*
> > > + * Internal Control Command
> > > + */
> > > +
> > > +#define CMD_0_ATTR_M FIELD_PREP(CMD_0_ATTR, 0x7)
> > > +
> > > +#define CMD_M1_VENDOR_SPECIFIC W1_MASK(63, 32)
> > > +#define CMD_M0_MIPI_RESERVED W0_MASK(31, 12)
> > > +#define CMD_M0_MIPI_CMD W0_MASK(11, 8)
> > > +#define CMD_M0_VENDOR_INFO_PRESENT W0_BIT_(7)
> > > +#define CMD_M0_TID(v) FIELD_PREP(W0_MASK(6, 3), v)
> > > +
> > > +
> > > +static int hci_cmd_v1_prep_ccc(struct i3c_hci *hci,
> > > + struct hci_xfer *xfer,
> > > + u8 ccc_addr, u8 ccc_cmd, bool raw)
> > > +{
> > > + u_int dat_idx = 0;
> >
> > I guess u_int her and below is not the preferred way to declare an unsigned int?
>
> Why not?
>
> > > + int mode = hci_get_i3c_mode(hci);
> > > + u8 *data = xfer->data;
> > > + u_int data_len = xfer->data_len;
> > > + bool rnw = xfer->rnw;
> > > + int ret;
> > > +
> > > + BUG_ON(raw);
> >
> > It looks like 'raw' cannot be used with v1 (at least you seem to take
> > care of it in v2), so maybe BUG_ON is a bit radical here and you can
> > simply return an error? I think the use of BUG() is not appreciated in
> > general.
>
> That depends. Judgement is needed for BUG() usage.
>
> Here raw is absolutely impossible with v1 hardware and if ever this
> happens this is definitely a software bug that needs fixing right away.
> There is no point returning a runtime error code in that case as the
> upper layer won't know what to do about it.
>
> On the other hand, you absolutely don't want to BUG() on a condition
> that could _eventually_ happen at run time during normal usage. But
> that's not the case here.

Well, people have tried to eradicate BUG() occurrences, so let's not add
new ones if we can avoid it. How about a WARN_ON()+error:

if (WARN_ON(raw))
return -EINVAL;

>
> > > +const struct hci_cmd_ops i3c_hci_cmd_v1 = {
> > > + .prep_ccc = hci_cmd_v1_prep_ccc,
> > > + .prep_i3c_xfer = hci_cmd_v1_prep_i3c_xfer,
> > > + .prep_i2c_xfer = hci_cmd_v1_prep_i2c_xfer,
> > > + .perform_daa = hci_cmd_v1_daa,
> >
> > I know Boris does not like such space alignment :)
>
> Well... unfortunately for Boris, this is overwhelmingly prevalent in the
> kernel code:
>
> $ git grep "^"$'\t'"\.[^ ]*"$'\t'"*= "
>
> And I do like it. ;-P

The rational being this preference is that sooner or later someone will
add a field to hci_cmd_ops that messes up your nice formatting :P.
Anyway, that's definitely not a blocker.

>
> > > +void i3c_hci_pio_reset(struct i3c_hci *hci)
> > > +{
> > > + reg_write(RESET_CONTROL, RX_FIFO_RST|TX_FIFO_RST|RESP_QUEUE_RST);
> >
> > Style with missing spaces ^ ^
>
> True. Will fix.
>
> > > +static int i3c_hci_send_ccc_cmd(struct i3c_master_controller *m,
> > > + struct i3c_ccc_cmd *ccc)
> > > +{
> > > + struct i3c_hci *hci = to_i3c_hci(m);
> > > + struct hci_xfer *xfer;
> > > + bool raw = !!(hci->quirks & HCI_QUIRK_RAW_CCC);
> > > + bool prefixed = raw && !!(ccc->id & I3C_CCC_DIRECT);
> > > + u_int nxfers = ccc->ndests + prefixed;
> > > + DECLARE_COMPLETION_ONSTACK(done);
> > > + int i, last, ret = 0;
> > > +
> > > + DBG("cmd=%#x rnw=%d ndests=%d data[0].len=%d",
> > > + ccc->id, ccc->rnw, ccc->ndests, ccc->dests[0].payload.len);
> > > +
> > > + xfer = hci_alloc_xfer(nxfers);
> > > + if (!xfer)
> > > + return -ENOMEM;
> > > +
> > > + if (prefixed) {
> > > + xfer->data = NULL;
> > > + xfer->data_len = 0;
> > > + xfer->rnw = false;
> > > + hci->cmd->prep_ccc(hci, xfer, I3C_BROADCAST_ADDR,
> > > + ccc->id, true);
> > > + xfer++;
> > > + }
> > > +
> > > + for (i = 0; i < nxfers - prefixed; i++) {
> > > + xfer[i].data = ccc->dests[i].payload.data;
> > > + xfer[i].data_len = ccc->dests[i].payload.len;
> > > + xfer[i].rnw = ccc->rnw;
> > > + ret = hci->cmd->prep_ccc(hci, &xfer[i], ccc->dests[i].addr,
> > > + ccc->id, raw);
> > > + if (ret)
> > > + goto out;
> > > + xfer[i].cmd_desc[0] |= CMD_0_ROC;
> > > + }
> > > + last = i - 1;
> > > + xfer[last].cmd_desc[0] |= CMD_0_TOC;
> > > + xfer[last].completion = &done;
> > > +
> > > + if (prefixed)
> > > + xfer--;
> > > +
> > > + ret = hci->io->queue_xfer(hci, xfer, nxfers);
> > > + if (ret)
> > > + goto out;
> > > + if (!wait_for_completion_timeout(&done, HZ) &&
> > > + hci->io->dequeue_xfer(hci, xfer, nxfers)) {
> > > + ret = -ETIME;
> > > + goto out;
> > > + }
> > > + for (i = prefixed; i < nxfers; i++) {
> > > + if (ccc->rnw)
> > > + ccc->dests[i - prefixed].payload.len =
> > > + RESP_DATA_LENGTH(xfer[i].response);
> > > + if (RESP_STATUS(xfer[i].response) != RESP_SUCCESS) {
> > > + ret = -EIO;
> > > + goto out;
> > > + }
> > > + }
> > > +
> > > +#if 0
> > > + if (ccc->rnw) {
> > > + HEXDUMP("got: ", ccc->dests[0].payload.data,
> > > + ccc->dests[0].payload.len);
> > > + }
> > > +#endif
> >
> > I guess this debug block can be dropped too (there are many debug
> > information the should probably be dropped or turned into dev_info()
> > or similar).
>
> Again, hardware bringup from different vendors and other developments
> are still ongoing. I'd wish for those to stay for the time being unless
> people feel strongly enough about these to become a merge show stopper.

Can't we replace that by a dev_dbg() using the %*pE formater?

>
> > > +/*
> > > + * Paul Kimelman's debug trace log facility.
> > > + * This is completely vendor and hardware specific.
> > > + */
> > > +void __PK_debug_trace(struct i3c_hci *hci, const char *func)
> > > +{
> > > + void __iomem *trcp = (void __iomem *)hci->vendor_data + 7*4;
> >
> > Maybe you need to define what is 7*4 , 0*4 below, v >> 27, etc
> >
> > Also there are many missing spaces between operators (7 * 4,w & (1 <<9).
>
> I think in this case this is really crossing the distraction threshold.
> This is used to extract debugging traces out of a specific FPGA
> implementation and is of no use to anyone else. I'll just rip that out
> from the next submission.
>
> > > + if (rh->ibi_data_phys)
> >
> > I was told that _phys was a very bad suffix for something which is a
> > DMA address an not focibly a physical address.
>
> Fair enough. The HCI spec refers to these as "physical memory" hence the
> suffix. What were you told to use instead?

Maybe _dma instead of _phys?

>
> > > +static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
> > > + struct hci_xfer *xfer_list, int n)
> > > +{
> > > + struct hci_rings_data *rings = hci->io_data;
> > > + struct hci_rh_data *rh = &rings->headers[xfer_list[0].ring];
> > > + u_int i;
> > > + bool did_unqueue = false;
> > > +
> > > + /* stop the ring */
> > > + rh_reg_write(RING_CONTROL, RING_CTRL_ABORT);
> > > + if (wait_for_completion_timeout(&rh->op_done, HZ) == 0) {
> > > + /*
> > > + * We're deep in it if ever this condition is ever met.
> > > + * Hardware might still be writing to memory, etc.
> > > + */
> > > + ERR("unable to abort the ring");
> > > + BUG();
> >
> > Why not just treating the error as always?
>
> Again, if this ever happens, you're screwed. That means potential DMA
> engines could still be alive and about to scribble over memory that is
> about to be freed which may cause all sorts of impossible-to-find bugs
> in unrelated parts of the kernel. There is no point going on reporting
> such error condition to upper layers until the software, or possibly the
> hardware, is fixed

Again, I think adding a WARN_ON() and letting hci_dma_dequeue_xfer()
return an error code is a good compromise.

>
> > > +struct hci_xfer {
> > > + u32 cmd_desc[4];
> > > + u32 response;
> > > + bool rnw;
> > > + void *data;
> > > + u_int data_len;
> > > + u_int cmd_tid;
> > > + struct completion *completion;
> > > + union {
> > > + struct {
> > > + /* PIO specific */
> > > + struct hci_xfer *next_xfer;
> > > + struct hci_xfer *next_data;
> > > + struct hci_xfer *next_resp;
> > > + u_int data_left;
> > > + u32 data_word_before_partial;
> > > + };
> >
> > I think anonymous unions are prohibited because the kernel is supposed
> > to be built with old gcc versions which do not support it.
>
> Hmmm... let's see:
>
> According to Documentation/process/changes.rst the current minimal
> required gcc version is 4.9.
>
> The oldest gcc I have lying around is 4.5.1 and it supports anonymous
> unions just fine.
>
> So I think we're clear.

We had problems with a buggy version of gcc 4.<something> at some
point, and that was only when initializing anonymous unions, but I
think it's all behind us now.