linux-kernel - Re: [PATCH 1/4] spi: s3c64xx: modified error interrupt handling and init

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Date:	Wed, 6 Feb 2013 23:48:38 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Girish KS <girishks2000@...il.com>
Cc:	spi-devel-general@...ts.sourceforge.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] spi: s3c64xx: modified error interrupt handling and init

On Wed, Feb 6, 2013 at 8:12 PM, Girish KS <girishks2000@...il.com> wrote:
> On Wed, Feb 6, 2013 at 2:26 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
>> On Tue,  5 Feb 2013 15:09:41 -0800, Girish K S <girishks2000@...il.com> wrote:
>>> The status of the interrupt is available in the status register,
>>> so reading the clear pending register and writing back the same
>>> value will not actually clear the pending interrupts. This patch
>>> modifies the interrupt handler to read the status register and
>>> clear the corresponding pending bit in the clear pending register.
>>>
>>> Modified the hwInit function to clear all the pending interrupts.
>>>
>>> Signed-off-by: Girish K S <ks.giri@...sung.com>
>>> ---
>>>  drivers/spi/spi-s3c64xx.c |   41 +++++++++++++++++++++++++----------------
>>>  1 file changed, 25 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>>> index ad93231..b770f88 100644
>>> --- a/drivers/spi/spi-s3c64xx.c
>>> +++ b/drivers/spi/spi-s3c64xx.c
>>> @@ -997,25 +997,30 @@ static irqreturn_t s3c64xx_spi_irq(int irq, void *data)
>>>  {
>>>       struct s3c64xx_spi_driver_data *sdd = data;
>>>       struct spi_master *spi = sdd->master;
>>> -     unsigned int val;
>>> +     unsigned int val, clr = 0;
>>>
>>> -     val = readl(sdd->regs + S3C64XX_SPI_PENDING_CLR);
>>> +     val = readl(sdd->regs + S3C64XX_SPI_STATUS);
>>>
>>> -     val &= S3C64XX_SPI_PND_RX_OVERRUN_CLR |
>>> -             S3C64XX_SPI_PND_RX_UNDERRUN_CLR |
>>> -             S3C64XX_SPI_PND_TX_OVERRUN_CLR |
>>> -             S3C64XX_SPI_PND_TX_UNDERRUN_CLR;
>>> -
>>> -     writel(val, sdd->regs + S3C64XX_SPI_PENDING_CLR);
>>> -
>>> -     if (val & S3C64XX_SPI_PND_RX_OVERRUN_CLR)
>>> +     if (val & S3C64XX_SPI_ST_RX_OVERRUN_ERR) {
>>> +             clr = S3C64XX_SPI_PND_RX_OVERRUN_CLR;
>>>               dev_err(&spi->dev, "RX overrun\n");
>>> -     if (val & S3C64XX_SPI_PND_RX_UNDERRUN_CLR)
>>> +     }
>>> +     if (val & S3C64XX_SPI_ST_RX_UNDERRUN_ERR) {
>>> +             clr |= S3C64XX_SPI_PND_RX_UNDERRUN_CLR;
>>>               dev_err(&spi->dev, "RX underrun\n");
>>> -     if (val & S3C64XX_SPI_PND_TX_OVERRUN_CLR)
>>> +     }
>>> +     if (val & S3C64XX_SPI_ST_TX_OVERRUN_ERR) {
>>> +             clr |= S3C64XX_SPI_PND_TX_OVERRUN_CLR;
>>>               dev_err(&spi->dev, "TX overrun\n");
>>> -     if (val & S3C64XX_SPI_PND_TX_UNDERRUN_CLR)
>>> +     }
>>> +     if (val & S3C64XX_SPI_ST_TX_UNDERRUN_ERR) {
>>> +             clr |= S3C64XX_SPI_PND_TX_UNDERRUN_CLR;
>>>               dev_err(&spi->dev, "TX underrun\n");
>>> +     }
>>> +
>>> +     /* Clear the pending irq by setting and then clearing it */
>>> +     writel(clr, sdd->regs + S3C64XX_SPI_PENDING_CLR);
>>> +     writel(clr & ~clr, sdd->regs + S3C64XX_SPI_PENDING_CLR);
>>
>> Wait, what?  clr & ~clr == 0   Always.  What are you actually trying to do here?
> The user manual says, wirting 1 to the pending clear register clears
> the interrupt (its not auto clear to 0). so i need to explicitly reset
> those bits thats what the 2nd write does

Then write 0. That's the result of what the code does anyway, but the
code as-written is nonsensical.

g.
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