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Message-ID: <CAPwEoQNZef_CeeCDNFGG4oJHCiM3MN9-juq+xX3hB5DKp4vorQ@mail.gmail.com>
Date: Tue, 25 Feb 2025 17:28:48 +0800
From: Stanley Chu <stanley.chuys@...il.com>
To: Frank Li <Frank.li@....com>
Cc: miquel.raynal@...tlin.com, alexandre.belloni@...tlin.com, robh@...nel.org,
krzk+dt@...nel.org, conor+dt@...nel.org, linux-i3c@...ts.infradead.org,
linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
tomer.maimon@...oton.com, kwliu@...oton.com, yschu@...oton.com
Subject: Re: [PATCH v4 3/5] i3c: master: svc: Fix npcm845 FIFO empty issue
On Tue, Feb 25, 2025 at 12:32 AM Frank Li <Frank.li@....com> wrote:
>
> On Mon, Feb 24, 2025 at 04:39:06PM +0800, Stanley Chu wrote:
> > From: Stanley Chu <yschu@...oton.com>
> >
> > I3C HW stalls the write transfer if the transmit FIFO becomes empty,
> > when new data is written to FIFO, I3C HW resumes the transfer but the
> > first transmitted data bit may have the wrong value.
> > Fill the FIFO in advance to prevent FIFO from becoming empty.
> >
> > Signed-off-by: Stanley Chu <yschu@...oton.com>
> > ---
> > drivers/i3c/master/svc-i3c-master.c | 44 ++++++++++++++++++++---------
> > 1 file changed, 31 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> > index 8834f87a4767..07506ae0f914 100644
> > --- a/drivers/i3c/master/svc-i3c-master.c
> > +++ b/drivers/i3c/master/svc-i3c-master.c
> > @@ -942,7 +942,7 @@ static int svc_i3c_master_do_daa_locked(struct svc_i3c_master *master,
> > u8 *addrs, unsigned int *count)
> > {
> > u64 prov_id[SVC_I3C_MAX_DEVS] = {}, nacking_prov_id = 0;
> > - unsigned int dev_nb = 0, last_addr = 0;
> > + unsigned int dev_nb = 0, last_addr = 0, dyn_addr;
> > u32 reg;
> > int ret, i;
> >
> > @@ -985,6 +985,17 @@ static int svc_i3c_master_do_daa_locked(struct svc_i3c_master *master,
> > if (SVC_I3C_MSTATUS_RXPEND(reg)) {
> > u8 data[6];
> >
> > + /*
> > + * One slave sends its ID to request for address assignment,
> > + * pre-filling the dynamic address can reduce SCL clock stalls
> > + * and also fix the SVC_I3C_QUIRK_FIFO_EMPTY quirk.
> > + */
> > + dyn_addr = i3c_master_get_free_addr(&master->base, last_addr + 1);
> > + if (dyn_addr < 0)
> > + return -ENOSPC;
> > +
> > + writel(dyn_addr, master->regs + SVC_I3C_MWDATAB);
> > +
>
> Although there is 64 clock time after issue do_daa, it is still better if
> prefill dyn_addr before sent do daa command?
>
> If add a debug message before i3c_master_get_free_addr(), does it trigger
> hardware issue?
>
> Frank
Ideally, prefilling before the processDAA command is better. However,
it requires an additional check to write the dyn_addr at the right time
because the driver needs to write the processDAA command twice for one
assignment
Prefilling here is safe and efficient because the FIFO starts filling
within a few hundred nanoseconds on the npcm845, which is significantly
faster compared to the 64 SCL clock cycles.
>
> > /*
> > * We only care about the 48-bit provisioned ID yet to
> > * be sure a device does not nack an address twice.
> > @@ -1063,21 +1074,16 @@ static int svc_i3c_master_do_daa_locked(struct svc_i3c_master *master,
> > if (ret)
> > break;
> >
> > - /* Give the slave device a suitable dynamic address */
> > - ret = i3c_master_get_free_addr(&master->base, last_addr + 1);
> > - if (ret < 0)
> > - break;
> > -
> > - addrs[dev_nb] = ret;
> > + addrs[dev_nb] = dyn_addr;
> > dev_dbg(master->dev, "DAA: device %d assigned to 0x%02x\n",
> > dev_nb, addrs[dev_nb]);
> > -
> > - writel(addrs[dev_nb], master->regs + SVC_I3C_MWDATAB);
> > last_addr = addrs[dev_nb++];
> > }
> >
> > /* Need manual issue STOP except for Complete condition */
> > svc_i3c_master_emit_stop(master);
> > + svc_i3c_master_flush_fifo(master);
> > +
> > return ret;
> > }
> >
> > @@ -1225,8 +1231,8 @@ static int svc_i3c_master_read(struct svc_i3c_master *master,
> > return offset;
> > }
> >
> > -static int svc_i3c_master_write(struct svc_i3c_master *master,
> > - const u8 *out, unsigned int len)
> > +static int svc_i3c_master_write(struct svc_i3c_master *master, const u8 *out,
> > + unsigned int len, bool last)
> > {
> > int offset = 0, ret;
> > u32 mdctrl;
> > @@ -1243,7 +1249,7 @@ static int svc_i3c_master_write(struct svc_i3c_master *master,
> > * The last byte to be sent over the bus must either have the
> > * "end" bit set or be written in MWDATABE.
> > */
> > - if (likely(offset < (len - 1)))
> > + if (likely(offset < (len - 1)) || !last)
> > writel(out[offset++], master->regs + SVC_I3C_MWDATAB);
> > else
> > writel(out[offset++], master->regs + SVC_I3C_MWDATABE);
> > @@ -1274,6 +1280,17 @@ static int svc_i3c_master_xfer(struct svc_i3c_master *master,
> > SVC_I3C_MCTRL_RDTERM(*actual_len),
> > master->regs + SVC_I3C_MCTRL);
> >
> > + if (svc_has_quirk(master, SVC_I3C_QUIRK_FIFO_EMPTY) && !rnw && xfer_len) {
> > + u32 len = min_t(u32, xfer_len, SVC_I3C_FIFO_SIZE);
> > +
> > + ret = svc_i3c_master_write(master, out, len,
> > + xfer_len <= SVC_I3C_FIFO_SIZE);
> > + if (ret < 0)
> > + goto emit_stop;
> > + xfer_len -= len;
> > + out += len;
> > + }
> > +
>
> The same here, you prefill data after issue sent out address, timing still
> tight, only 9 SCL clock time. should it prefill before issue address?
>
> Frank
The entire transaction can consist of multiple read and write
transfers. In the case
of S+7E/W+Sr+dyn_addr/W+data+P, If the data is prefilled before Sr, it
will be emitted
immediately and become part of the previous transfer.
It is not a problem to fill FIFO here, the reason is the same as above.
I will also modify the code as below to make it efficient and keep
svc_i3c_master_write unchanged.
if (svc_has_quirk(master, SVC_I3C_QUIRK_FIFO_EMPTY) &&
!rnw && xfer_len) {
u32 len = min_t(u32, xfer_len, SVC_I3C_FIFO_SIZE);
while (len--) {
if (xfer_len == 1)
writel(out[0], master->regs +
SVC_I3C_MWDATABE);
else
writel(out[0], master->regs +
SVC_I3C_MWDATAB);
xfer_len--;
out++;
}
}
>
> > ret = readl_poll_timeout(master->regs + SVC_I3C_MSTATUS, reg,
> > SVC_I3C_MSTATUS_MCTRLDONE(reg), 0, 1000);
> > if (ret)
> > @@ -1335,7 +1352,7 @@ static int svc_i3c_master_xfer(struct svc_i3c_master *master,
> > if (rnw)
> > ret = svc_i3c_master_read(master, in, xfer_len);
> > else
> > - ret = svc_i3c_master_write(master, out, xfer_len);
> > + ret = svc_i3c_master_write(master, out, xfer_len, true);
> > if (ret < 0)
> > goto emit_stop;
> >
> > @@ -1362,6 +1379,7 @@ static int svc_i3c_master_xfer(struct svc_i3c_master *master,
> > emit_stop:
> > svc_i3c_master_emit_stop(master);
> > svc_i3c_master_clear_merrwarn(master);
> > + svc_i3c_master_flush_fifo(master);
> >
> > return ret;
> > }
> > --
> > 2.34.1
> >
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