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Message-ID: <CAHO=5PGzk6999KZ+bkDvUn5o0sYt4aYo-k-Qe37pRtrahx3FRg@mail.gmail.com>
Date: Mon, 26 Oct 2020 19:25:22 +0530
From: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
To: Ray Jui <ray.jui@...adcom.com>
Cc: Dhananjay Phadke <dphadke@...ux.microsoft.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
Brendan Higgins <brendanhiggins@...gle.com>,
Florian Fainelli <f.fainelli@...il.com>,
linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
linux-i2c <linux-i2c@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Lori Hikichi <lori.hikichi@...adcom.com>,
Ray Jui <rjui@...adcom.com>,
Scott Branden <sbranden@...adcom.com>,
Wolfram Sang <wsa@...nel.org>
Subject: Re: [PATCH v1 5/6] i2c: iproc: handle master read request
On Fri, Oct 23, 2020 at 10:56 PM Ray Jui <ray.jui@...adcom.com> wrote:
>
>
>
> On 10/13/2020 10:12 PM, Rayagonda Kokatanur wrote:
> >
> >
> > On Wed, Oct 14, 2020 at 8:50 AM Dhananjay Phadke
> > <dphadke@...ux.microsoft.com <mailto:dphadke@...ux.microsoft.com>> wrote:
> >
> > On Sun, 11 Oct 2020 23:52:53 +0530, Rayagonda Kokatanur wrote:
> > > --- a/drivers/i2c/busses/i2c-bcm-iproc.c
> > > +++ b/drivers/i2c/busses/i2c-bcm-iproc.c
> > >
> > > - } else if (status & BIT(IS_S_RD_EVENT_SHIFT)) {
> > > - /* Start of SMBUS for Master Read */
> > > + I2C_SLAVE_WRITE_REQUESTED,
> > &rx_data);
> > > + iproc_i2c->rx_start_rcvd = true;
> > > + iproc_i2c->slave_read_complete = false;
> > > + } else if (rx_status == I2C_SLAVE_RX_DATA &&
> > > + iproc_i2c->rx_start_rcvd) {
> > > + /* Middle of SMBUS Master write */
> > > i2c_slave_event(iproc_i2c->slave,
> > > - I2C_SLAVE_READ_REQUESTED,
> > &value);
> > > - iproc_i2c_wr_reg(iproc_i2c, S_TX_OFFSET, value);
> > > + I2C_SLAVE_WRITE_RECEIVED,
> > &rx_data);
> > > + } else if (rx_status == I2C_SLAVE_RX_END &&
> > > + iproc_i2c->rx_start_rcvd) {
> > > + /* End of SMBUS Master write */
> > > + if (iproc_i2c->slave_rx_only)
> > > + i2c_slave_event(iproc_i2c->slave,
> > > +
> > I2C_SLAVE_WRITE_RECEIVED,
> > > + &rx_data);
> > > +
> > > + i2c_slave_event(iproc_i2c->slave,
> > I2C_SLAVE_STOP,
> > > + &rx_data);
> > > + } else if (rx_status == I2C_SLAVE_RX_FIFO_EMPTY) {
> > > + iproc_i2c->rx_start_rcvd = false;
> > > + iproc_i2c->slave_read_complete = true;
> > > + break;
> > > + }
> > >
> > > - val = BIT(S_CMD_START_BUSY_SHIFT);
> > > - iproc_i2c_wr_reg(iproc_i2c, S_CMD_OFFSET, val);
> > > + rx_bytes++;
> >
> > rx_bytes should be incremented only along with
> > I2C_SLAVE_WRITE_RECEIVED event?
> >
> >
> > It should be incremented in both I2C_SLAVE_WRITE_REQUESTED and
> > I2C_SLAVE_WRITE_RECEIVED cases because in both case it is reading valid
> > bytes from rx fifo.
> >
> >
> > >
> > > +static bool bcm_iproc_i2c_slave_isr(struct bcm_iproc_i2c_dev
> > *iproc_i2c,
> > > + u32 status)
> > > +{
> > > + u32 val;
> > > + u8 value;
> > > +
> > > + /*
> > > + * Slave events in case of master-write, master-write-read and,
> > > + * master-read
> > > + *
> > > + * Master-write : only IS_S_RX_EVENT_SHIFT event
> > > + * Master-write-read: both IS_S_RX_EVENT_SHIFT and
> > IS_S_RD_EVENT_SHIFT
> > > + * events
> > > + * Master-read : both IS_S_RX_EVENT_SHIFT and
> > IS_S_RD_EVENT_SHIFT
> > > + * events or only IS_S_RD_EVENT_SHIFT
> > > + */
> > > + if (status & BIT(IS_S_RX_EVENT_SHIFT) ||
> > > + status & BIT(IS_S_RD_EVENT_SHIFT)) {
> > > + /* disable slave interrupts */
> > > + val = iproc_i2c_rd_reg(iproc_i2c, IE_OFFSET);
> > > + val &= ~iproc_i2c->slave_int_mask;
> > > + iproc_i2c_wr_reg(iproc_i2c, IE_OFFSET, val);
> > > +
> > > + if (status & BIT(IS_S_RD_EVENT_SHIFT))
> > > + /* Master-write-read request */
> > > + iproc_i2c->slave_rx_only = false;
> > > + else
> > > + /* Master-write request only */
> > > + iproc_i2c->slave_rx_only = true;
> > > +
> > > + /* schedule tasklet to read data later */
> > > + tasklet_schedule(&iproc_i2c->slave_rx_tasklet);
> > > +
> > > + /* clear only IS_S_RX_EVENT_SHIFT interrupt */
> > > + iproc_i2c_wr_reg(iproc_i2c, IS_OFFSET,
> > > + BIT(IS_S_RX_EVENT_SHIFT));
> > >
> >
> > Both tasklet and isr are writing to status (IS_OFFSET) reg.
> >
> >
> > Yes this is required.
> >
> > For ex, If IS_S_RD_EVENT_SHIFT interrupt, this should be cleared once
> > the driver completes reading all data from rx fifo.
> > After this the driver can start sending data to master.
> >
>
> If both tasklet and isr are accessing the IS_OFFSET register, don't you
> need lock protection against race condition? That is, ISR can interrupt
> tasklet.
All interrupts are disbaled when the tasklet is running.
Interrupts are re-enabled at the end of the tasklet.
So no race condition between tasklet and isr.
Best regards,
Rayagonda
>
> >
> >
> > The tasklet seems to be batching up rx fifo reads because of
> > time-sensitive
> > Master-write-read transaction? Linux I2C framework is byte interface
> > anyway.
> > Can the need to batch reads be avoided by setting slave rx threshold for
> > interrupt (S_FIFO_RX_THLD) to 1-byte?
> >
> >
> > To process more data with a single interrupt we are batching up rx fifo
> > reads.
> > This will reduce the number of interrupts.
> >
> > Also to avoid tasklet running more time (20us) we have a threshold of 10
> > bytes for batching read.
> > This is a better/optimised approach than reading single byte data per
> > interrupt.
> >
> >
> > Also, wouldn't tasklets be susceptible to other interrupts? If fifo
> > reads
> > have to be batched up, can it be changed to threaded irq?
> >
> >
> > tasklets have higher priority than threaded irq, since i2c is time
> > sensitive so using a tasklet is preferred over threaded irq.
> >
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