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 */ > > This definitely looks wrong. The check whether the interrupt is enabled > should be moved *before* the conditional calls to bcm2835_rd_fifo_blind() > and bcm2835_wr_fifo_blind(), i.e. to the top of the function. > > Otherwise if an interrupt is raised by another SPI controller, > this function may perform read/write accesses to the FIFO and > interfere with an ongoing transfer in DMA or poll mode. > > Also, instead of performing an MMIO read, just use the "cs" variable > which was assigned at the top of the function. > > The code comment should explain that the check is necessary because the > interrupt may be shared with other controllers on the BCM2711. > > 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. -- Florian
