Messages in this thread | | | Subject | Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support | From | Robin Murphy <> | Date | Fri, 5 Jun 2020 12:34:36 +0100 |
| |
On 2020-06-04 22:28, Florian Fainelli wrote: > The 4 SPI controller instances added in BCM2711 and BCM7211 SoCs (SPI3, > SPI4, SPI5 and SPI6) share the same interrupt line with SPI0. > > For the BCM2835 case which is deemed performance critical, we would like > to continue using an interrupt handler which does not have the extra > comparison on BCM2835_SPI_CS_INTR.
FWIW, if I'm reading the patch correctly, then with sensible codegen that "overhead" should amount to a bit test on a live register plus a not-taken conditional branch - according to the 1176 TRM that should add up to a whopping 2 cycles. If that's really significant then I'd have to wonder whether you want to be at the mercy of the whole generic IRQ stack at all, and should perhaps consider using FIQ instead.
> To support that requirement the common interrupt handling code between > the shared and non-shared interrupt paths is split into a > bcm2835_spi_interrupt_common() and both bcm2835_spi_interrupt() as well > as bcm2835_spi_shared_interrupt() make use of it. > > During probe, we determine if there is at least another instance of this > SPI controller, and if there is, then we install a shared interrupt > handler. > > Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> > --- > Changes in v2: > > - identify other available SPI nodes to determine if we need to set-up > interrupt sharing. This needs to happen for the very first instance > since we cannot know for the first instance whether interrupt sharing > is needed or not. > > drivers/spi/spi-bcm2835.c | 61 ++++++++++++++++++++++++++++++++------- > 1 file changed, 50 insertions(+), 11 deletions(-) > > diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c > index 237bd306c268..0288b5b3de1e 100644 > --- a/drivers/spi/spi-bcm2835.c > +++ b/drivers/spi/spi-bcm2835.c > @@ -361,11 +361,10 @@ static void bcm2835_spi_reset_hw(struct spi_controller *ctlr) > bcm2835_wr(bs, BCM2835_SPI_DLEN, 0); > } > > -static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > +static inline irqreturn_t bcm2835_spi_interrupt_common(struct spi_controller *ctlr, > + u32 cs) > { > - struct spi_controller *ctlr = dev_id; > struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > - u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > > /* > * An interrupt is signaled either if DONE is set (TX FIFO empty) > @@ -394,6 +393,27 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > return IRQ_HANDLED; > } > > +static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) > +{ > + struct spi_controller *ctlr = dev_id; > + struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > + u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > + > + return bcm2835_spi_interrupt_common(ctlr, cs); > +} > + > +static irqreturn_t bcm2835_spi_shared_interrupt(int irq, void *dev_id) > +{ > + struct spi_controller *ctlr = dev_id; > + struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); > + u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); > + > + if (!(cs & BCM2835_SPI_CS_INTR)) > + return IRQ_NONE; > + > + return bcm2835_spi_interrupt_common(ctlr, cs); > +} > + > static int bcm2835_spi_transfer_one_irq(struct spi_controller *ctlr, > struct spi_device *spi, > struct spi_transfer *tfr, > @@ -1287,12 +1307,37 @@ static int bcm2835_spi_setup(struct spi_device *spi) > return 0; > } > > +static const struct of_device_id bcm2835_spi_match[] = { > + { .compatible = "brcm,bcm2835-spi", }, > + {} > +}; > +MODULE_DEVICE_TABLE(of, bcm2835_spi_match); > + > static int bcm2835_spi_probe(struct platform_device *pdev) > { > + irq_handler_t bcm2835_spi_isr_func = bcm2835_spi_interrupt; > struct spi_controller *ctlr; > + unsigned long flags = 0; > + struct device_node *dn; > struct bcm2835_spi *bs; > int err; > > + /* On BCM2711 there can be multiple SPI controllers enabled sharing the > + * same interrupt line, but we also want to minimize the overhead if > + * there is no need to support interrupt sharing. If we find at least > + * another available instane (not counting the one we are probed from), > + * then we assume that interrupt sharing is necessary. > + */ > + for_each_compatible_node(dn, NULL, bcm2835_spi_match[0].compatible) { > + err = of_device_is_available(dn) && dn != pdev->dev.of_node; > + of_node_put(dn);
This is in the wrong place - it should only be where you terminate the loop early and thus bypass the "of_node_put(from)" call in the iterator itself.
> + if (err) { > + flags = IRQF_SHARED;
Is there really any harm to setting IRQF_SHARED even when the interrupt isn't shared in hardware? Sure, it means you lose a degree of API-level validation and some other driver might also be able to simultaneously claim it on bcm283x, but in that case the DT would be wrong and *something* isn't going to work correctly anyway, so does this one driver really need to care about trying to be the DT police?
Robin.
> + bcm2835_spi_isr_func = bcm2835_spi_shared_interrupt; > + break; > + } > + } > + > ctlr = spi_alloc_master(&pdev->dev, ALIGN(sizeof(*bs), > dma_get_cache_alignment())); > if (!ctlr) > @@ -1344,8 +1389,8 @@ static int bcm2835_spi_probe(struct platform_device *pdev) > bcm2835_wr(bs, BCM2835_SPI_CS, > BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX); > > - err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt, 0, > - dev_name(&pdev->dev), ctlr); > + err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_isr_func, > + flags, dev_name(&pdev->dev), ctlr); > if (err) { > dev_err(&pdev->dev, "could not request IRQ: %d\n", err); > goto out_dma_release; > @@ -1400,12 +1445,6 @@ static void bcm2835_spi_shutdown(struct platform_device *pdev) > dev_err(&pdev->dev, "failed to shutdown\n"); > } > > -static const struct of_device_id bcm2835_spi_match[] = { > - { .compatible = "brcm,bcm2835-spi", }, > - {} > -}; > -MODULE_DEVICE_TABLE(of, bcm2835_spi_match); > - > static struct platform_driver bcm2835_spi_driver = { > .driver = { > .name = DRV_NAME, >
| |