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Message-ID: <73535dcc422441d3a981208dae1a2bad@bgmail102.nvidia.com>
Date: Sat, 16 Apr 2016 08:08:50 +0000
From: Shardar Mohammed <smohammed@...dia.com>
To: Thierry Reding <thierry.reding@...il.com>,
Shardar Mohammed <smohammed@...dia.com>
CC: Laxman Dewangan <ldewangan@...dia.com>,
"swarren@...dotorg.org" <swarren@...dotorg.org>,
"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"wsa@...-dreams.de" <wsa@...-dreams.de>,
"gnurou@...il.com" <gnurou@...il.com>
Subject: RE: [PATCH] i2c: tegra: proper handling of error cases
Thanks for the review, updated with comments inline with Shardar.
> On Fri, Apr 15, 2016 at 06:51:47PM +0530, Shardar Shariff Md wrote:
> > From: Shardar Shariff Md <smohammed@...dia.com>
> >
> > To summarize the issue observed in error cases:
> >
> > In SW: For i2c message transfer, packet header and data payload is
> > posted and then required error/packet completion interrupts are
> > enabled later.
> >
> > In HW flow: HW process the packet just after packet header is posted,
> > if ARB lost/NACK error occurs (SW will not handle immediately when
> > error happens as error interrupts are not enabled at this point). HW
> > assumes error is acknowledged and clears current data in FIFO, But SW
> > here posts the remaining data payload which still stays in FIFO as
> > stale data (data without packet header).
> >
> > Now once the interrupts are enabled, SW handles ARB lost/NACK error by
> > clearing the ARB lost/NACK interrupt. Now HW assumes that SW attended
> > the error and will parse/process stale data (data without packet
> > header) present in FIFO which causes invalid NACK errors.
> >
> > Fix: Enable the error interrupts before posting the packet into FIFO
> > which make sure HW to not clear the fifo. Also disable the packet mode
> > before acknowledging errors (ARB lost/NACK error) to not process any
> > stale data.
> >
> > As error interrupts are enabled before posting the packet header use
> > spinlock to avoid preempting.
>
> Please try to use up the full 78 characters per line in the commit message
> (with the exception being the subject line that should be shorter).
[Shardar] Will take care of this.
> > diff --git a/drivers/i2c/busses/i2c-tegra.c
> > b/drivers/i2c/busses/i2c-tegra.c
> [...]
> > @@ -423,12 +424,31 @@ static inline void tegra_i2c_clock_disable(struct
> tegra_i2c_dev *i2c_dev)
> > clk_disable(i2c_dev->fast_clk);
> > }
> >
> > +static int tegra_i2c_wait_for_config_load(struct tegra_i2c_dev
> > +*i2c_dev) {
> > + unsigned long timeout;
> > +
> > + if (i2c_dev->hw->has_config_load_reg) {
> > + i2c_writel(i2c_dev, I2C_MSTR_CONFIG_LOAD,
> I2C_CONFIG_LOAD);
> > + timeout = jiffies + msecs_to_jiffies(1000);
> > + while (i2c_readl(i2c_dev, I2C_CONFIG_LOAD) != 0) {
> > + if (time_after(jiffies, timeout)) {
> > + dev_warn(i2c_dev->dev,
> > + "timeout waiting for config load\n");
>
> Nit: since you're already changing this, perhaps make the arguments on
> subsequent lines align with the first argument on the first line? Like
> so:
>
> dev_warn(i2c_dev->dev,
> "timeout waiting for config load\n");
>
> Note the extra space used for padding.
>
[Shardar] Will take care of this.
> > + return -ETIMEDOUT;
> > + }
> > + msleep(1);
> > + }
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev) {
> > u32 val;
> > int err = 0;
> > u32 clk_divisor;
> > - unsigned long timeout = jiffies + HZ;
> >
> > err = tegra_i2c_clock_enable(i2c_dev);
> > if (err < 0) {
> > @@ -477,20 +497,13 @@ static int tegra_i2c_init(struct tegra_i2c_dev
> *i2c_dev)
> > if (i2c_dev->is_multimaster_mode && i2c_dev->hw-
> >has_slcg_override_reg)
> > i2c_writel(i2c_dev, I2C_MST_CORE_CLKEN_OVR,
> I2C_CLKEN_OVERRIDE);
> >
> > - if (i2c_dev->hw->has_config_load_reg) {
> > - i2c_writel(i2c_dev, I2C_MSTR_CONFIG_LOAD,
> I2C_CONFIG_LOAD);
> > - while (i2c_readl(i2c_dev, I2C_CONFIG_LOAD) != 0) {
> > - if (time_after(jiffies, timeout)) {
> > - dev_warn(i2c_dev->dev,
> > - "timeout waiting for config load\n");
> > - return -ETIMEDOUT;
> > - }
> > - msleep(1);
> > - }
> > - }
> > + err = tegra_i2c_wait_for_config_load(i2c_dev);
> >
> > tegra_i2c_clock_disable(i2c_dev);
> >
> > + if (err)
> > + return err;
> > +
>
> The behaviour here is now different, though I assume it's really a fix that
> disables the I2C clock in case the timeout happens. Given that I suspect this
> would be better off in a separate patch (factor out the
> tegra_i2c_wait_for_config_load() function and return error after the clocks
> have been disabled).
[Shardar] Will take care of this.
>
> > if (i2c_dev->irq_disabled) {
> > i2c_dev->irq_disabled = 0;
> > enable_irq(i2c_dev->irq);
> > @@ -499,14 +512,28 @@ static int tegra_i2c_init(struct tegra_i2c_dev
> *i2c_dev)
> > return err;
> > }
> >
> > +static int tegra_i2c_disable_packet_mode(struct tegra_i2c_dev
> > +*i2c_dev) {
> > + u32 cnfg;
> > +
> > + cnfg = i2c_readl(i2c_dev, I2C_CNFG);
> > + if (cnfg & I2C_CNFG_PACKET_MODE_EN)
> > + i2c_writel(i2c_dev, cnfg & (~I2C_CNFG_PACKET_MODE_EN),
>
> Parentheses are not necessary here.
>
> > + I2C_CNFG);
>
> If you drop the parentheses above this can be moved into the previous line
> because it will fit within 80 columns.
[Shardar] Will take care of this.
>
> > +
> > + return tegra_i2c_wait_for_config_load(i2c_dev);
> > +}
> > +
> > static irqreturn_t tegra_i2c_isr(int irq, void *dev_id) {
> > u32 status;
> > const u32 status_err = I2C_INT_NO_ACK |
> I2C_INT_ARBITRATION_LOST;
> > struct tegra_i2c_dev *i2c_dev = dev_id;
> > + unsigned long flags;
> >
> > status = i2c_readl(i2c_dev, I2C_INT_STATUS);
> >
> > + spin_lock_irqsave(&i2c_dev->xfer_lock, flags);
> > if (status == 0) {
> > dev_warn(i2c_dev->dev, "irq status 0 %08x %08x %08x\n",
> > i2c_readl(i2c_dev, I2C_PACKET_TRANSFER_STATUS),
> @@ -522,6 +549,7
> > @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
> > }
> >
> > if (unlikely(status & status_err)) {
> > + tegra_i2c_disable_packet_mode(i2c_dev);
>
> If you don't care about the return value it'd be better to reflect that by
> making the function return void. I presume ignoring the error here is safe?
[Shardar] Will take care of handling the return valure.
>
> > @@ -583,6 +614,11 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev
> *i2c_dev,
> > i2c_dev->msg_read = (msg->flags & I2C_M_RD);
> > reinit_completion(&i2c_dev->msg_complete);
> >
> > + spin_lock_irqsave(&i2c_dev->xfer_lock, flags);
> > +
> > + int_mask = I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST;
> > + tegra_i2c_unmask_irq(i2c_dev, int_mask);
> > +
> > packet_header = (0 << PACKET_HEADER0_HEADER_SIZE_SHIFT) |
> > PACKET_HEADER0_PROTOCOL_I2C |
> > (i2c_dev->cont_id <<
> PACKET_HEADER0_CONT_ID_SHIFT) | @@ -612,14
> > +648,15 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
> > if (!(msg->flags & I2C_M_RD))
> > tegra_i2c_fill_tx_fifo(i2c_dev);
> >
> > - int_mask = I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST;
> > if (i2c_dev->hw->has_per_pkt_xfer_complete_irq)
> > int_mask |= I2C_INT_PACKET_XFER_COMPLETE;
> > if (msg->flags & I2C_M_RD)
> > int_mask |= I2C_INT_RX_FIFO_DATA_REQ;
> > else if (i2c_dev->msg_buf_remaining)
> > int_mask |= I2C_INT_TX_FIFO_DATA_REQ;
> > +
> > tegra_i2c_unmask_irq(i2c_dev, int_mask);
>
> Can this line be removed? The NO_ACK and ARBITRATION_LOST interrupts
> are already unmasked earlier.
[Shardar] unmask_irq() here is enabling other interrupts (PACKET_XFER_COMPLETE/TX_FIFO_DATA_REQ/RX_FIFO_DATA_REQ). please let me know if my understanding is wrong from your comment.
>
> Thierry
>
> * Unknown Key
> * 0x7F3EB3A1
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