[PATCH 1/4] spi: s3c64xx: modified error interrupt handling and init

[Girish KS]

On Fri, Feb 8, 2013 at 12:33 AM, Tomasz Figa <tomasz.figa at gmail.com> wrote:
> On Thursday 07 of February 2013 09:46:58 Girish KS wrote:
>> On Thu, Feb 7, 2013 at 3:09 AM, Tomasz Figa <t.figa at samsung.com> wrote:
>> > Hi Girish,
>> >
>> > On Wednesday 06 of February 2013 12:12:29 Girish KS wrote:
>> >> On Wed, Feb 6, 2013 at 2:26 AM, Grant Likely
>> >> <grant.likely at secretlab.ca>>
>> > wrote:
>> >> > On Tue,  5 Feb 2013 15:09:41 -0800, Girish K S
>> >
>> > <girishks2000 at gmail.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 at samsung.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
>> >
>> > I have looked through user's manuals of different Samsung SoCs. All of
>> > them said that writing 1 to a bit clears the corresponding interrupt,
>> > but none of them contain any note that it must be manually cleared to
>> > 0.
>> What i meant was the clear pending bit will not clear automatically.
>> When I set the
>> clear pending bit, it remains set. This is a problem for the next
>> interrupt cycle.
>
> How did you check that it does not clear automatically?
I checked it with trace32 debugger. Also  confirmed with the IP
validation engineer.
>
>> > In addition the expression
>> >
>> > clr & ~clr
>> >
>> > makes no sense, because it is equal to 0.
>>
>> It makes sense, because we are not disturbing the interrupt pending
>> bit at position 0, which is a trailing clr bit.
>
> You either seem to misunderstand the problem I'm mentioning or not
> understanding it at all.
>
> If you take a variable named clr, no matter what value it is set to, and
> you AND it with bitwise negation of the same variable, you will get 0.
>
> See on this example:
>
> Bits:     7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
>          -------------------------------
> Values:   1 | 1 | 0 | 0 | 1 | 0 | 0 | 1
>          -------------------------------
> Negation: 0 | 0 | 1 | 1 | 0 | 1 | 1 | 0
>          -------------------------------
> AND:      0 | 0 | 0 | 0 | 0 | 0 | 0 | 0
>
> Now, can you see that (clr & ~clr) is the same as (0)?

Already apolozised for the same: will resubmit.

>
> Best regards,
> Tomasz
>