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SubjectRe: [PATCH] spi: bcm2835: Enable shared interrupt support
On Fri, May 29, 2020 at 10:46:01AM -0700, Florian Fainelli wrote:
> On 5/29/20 10:43 AM, Lukas Wunner wrote:
> > On Thu, May 28, 2020 at 08:58:04PM +0200, Nicolas Saenz Julienne wrote:
> >> --- a/drivers/spi/spi-bcm2835.c
> >> +++ b/drivers/spi/spi-bcm2835.c
> >> @@ -379,6 +379,10 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id)
> >> if (bs->tx_len && cs & BCM2835_SPI_CS_DONE)
> >> bcm2835_wr_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE);
> >>
> >> + /* check if we got interrupt enabled */
> >> + if (!(bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_INTR))
> >> + return IRQ_NONE;
> >> +
> >> /* Read as many bytes as possible from FIFO */
> >> bcm2835_rd_fifo(bs);
> >> /* Write as many bytes as possible to FIFO */
[...]
> > Finally, it would be nice if the check would be optimized away when
> > compiling for pre-RasPi4 products, maybe something like:
> >
> > + if (IS_ENABLED(CONFIG_ARM_LPAE) && !(cs & BCM2835_SPI_CS_INTR))
> > + return IRQ_NONE;
>
> Rather than keying this off ARM_LPAE or any other option, this should be
> keyed off a compatible string, that way we can even conditionally pass
> IRQF_SHARED to the interrupt handler if we care so much about performance.

But a compatible string can't be checked at compile time, can it?

The point is that at the least the Foundation compiles and ships a separate
kernel for each of the three platforms BCM2835, BCM2837, BCM2711. It's
unnecessary to check whether an interrupt was actually raised if we *know*
in advance that it's not shared (as is the case with kernels compiled for
BCM2835 and BCM2837).

Thanks,

Lukas

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