linux-kernel - RE: [PATCH V13 3/5] i2c: tegra: Add DMA support

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Date:   Wed, 6 Feb 2019 16:56:15 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Dmitry Osipenko <digetx@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>,
        "Shardar Mohammed" <smohammed@...dia.com>,
        Timo Alho <talho@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH V13 3/5] i2c: tegra: Add DMA support

> > > >> Looking into timestamps and transactions, DMA timeouts after start of DMA for I2C1 to touch during this transaction.
> > > >> While it is waiting for I2C1 DMA transfer, lots of DVC 
> > > >> transactions happened thru DMA which are successful
> > > >>
> > > >> What is the I2C1 speed?
> > > > 
> > > > 400KHz
> > > > 
> > > >> Also incase if device is running slow for some reason, probably timeout was not enough as this patch series changes timeout with base 100mS + msg transfer time based on transfer size.
> > > >> Can you give quick try with increased timeout incase if device is running slow?
> > > >>
> > > > 
> > > > Tried to increase the timeout to 1 second, doesn't help.
> > > > 
> > > > What helped again is the I2C HW resetting after each transfer. Likely that means that HW isn't programmed correctly, please carefully check every bit.
> > > > 
> > > > DMA-only + I2C HW reset: http://dpaste.com/26AQXFM.txt
> > >
> > > Seems I found what's the problem. Here is the fix, please include it to v14 if it is correct.
> > >
> > > diff --git a/drivers/i2c/busses/i2c-tegra.c 
> > > b/drivers/i2c/busses/i2c-tegra.c index a9391c3646b6..5ad54da70304 
> > > 100644
> > > --- a/drivers/i2c/busses/i2c-tegra.c
> > > +++ b/drivers/i2c/busses/i2c-tegra.c
> > > @@ -912,7 +912,7 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)  static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
> > >                                        size_t len)  {
> > > -       u32 val, reg;
> > > +       u32 val = 0, reg;
> > >         u8 dma_burst = 0;
> > >         struct dma_slave_config slv_config = {0};
> > >         struct dma_chan *chan;
> > > @@ -922,7 +922,6 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
> > >                 reg = I2C_MST_FIFO_CONTROL;
> > >         else
> > >                 reg = I2C_FIFO_CONTROL;
> > > -       val = i2c_readl(i2c_dev, reg);
> >  >
> >  >        if (i2c_dev->is_curr_dma_xfer) {
> >  >                if (len & 0xF)
> > 
> > Thanks dmitry. Good catch. Didn't caught to my eyes. Yes FIFO_CONTROL 
> > is set based on read value without masking and oring causing back-back DMA transfers resulting in incorrect trig levels We can directly set trig levels.
>
> It might be safer to explicitly clear the trigger levels before we overwrite them. Though, admittedly, this register hasn't changed in years, so it's unlikely we'll ever see it change in a way that might result in breakage if we construct the register value from scratch.
>
> Thierry

FIFO_CONTROL has trig and flush for TX & RX and since we do TX/RX and flush anyway prior to transfer, constructing from scratch should be fine as its same as doing mask-modify-write