Hi Saravana, On Thu, Feb 18, 2021 at 12:57 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > On Tue, Feb 16, 2021 at 12:31 PM Geert Uytterhoeven > <geert@xxxxxxxxxxxxxx> wrote: > > On Tue, Feb 16, 2021 at 7:49 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > On Tue, Feb 16, 2021 at 12:05 AM Geert Uytterhoeven > > > <geert@xxxxxxxxxxxxxx> wrote: > > > > On Mon, Feb 15, 2021 at 10:27 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > On Mon, Feb 15, 2021 at 4:38 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > > > > > On Fri, Feb 12, 2021 at 4:00 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > > > On Thu, Feb 11, 2021 at 5:00 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > > > > > > > - I2C on R-Car Gen3 does not seem to use DMA, according to > > > > > > > > /sys/kernel/debug/dmaengine/summary: > > > > > > > > > > > > > > > > -dma4chan0 | e66d8000.i2c:tx > > > > > > > > -dma4chan1 | e66d8000.i2c:rx > > > > > > > > -dma5chan0 | e6510000.i2c:tx > > > > > > > > > > > > > > I think I need more context on the problem before I can try to fix it. > > > > > > > I'm also very unfamiliar with that file. With fw_devlink=permissive, > > > > > > > I2C was using DMA? If so, the next step is to see if the I2C relative > > > > > > > probe order with DMA is getting changed and if so, why. > > > > > > > > > > > > More detailed log: > > > > > > > > > > > > platform e66d8000.i2c: Linked as a consumer to e6150000.clock-controller > > > > > > platform e66d8000.i2c: Linked as a sync state only consumer to e6055400.gpio > > > > > > > > > > > > Why is e66d8000.i2c not linked as a consumer to e6700000.dma-controller? > > > > > > > > > > Because fw_devlink.strict=1 is not set and dma/iommu is considered an > > > > > "optional"/"driver decides" dependency. > > > > > > > > Oh, I thought dma/iommu were considered mandatory initially, > > > > but dropped as dependencies in the late boot process? > > > > > > No, I didn't do that in case the drivers that didn't need the > > > IOMMU/DMA were sensitive to probe order. > > > > > > My goal was for fw_devlink=on to not affect probe order for devices > > > that currently don't need to defer probe. But see below... > > > > > > > > > > > > > > > > > > platform e6700000.dma-controller: Linked as a consumer to > > > > > > e6150000.clock-controller > > > > > > > > > > Is this the only supplier of dma-controller? > > > > > > > > No, e6180000.system-controller is also a supplier. > > > > > > > > > > platform e66d8000.i2c: Added to deferred list > > > > > > platform e6700000.dma-controller: Added to deferred list > > > > > > > > > > > > bus: 'platform': driver_probe_device: matched device > > > > > > e6700000.dma-controller with driver rcar-dmac > > > > > > bus: 'platform': really_probe: probing driver rcar-dmac with > > > > > > device e6700000.dma-controller > > > > > > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > > > > > > > > > > > > bus: 'platform': driver_probe_device: matched device e66d8000.i2c > > > > > > with driver i2c-rcar > > > > > > bus: 'platform': really_probe: probing driver i2c-rcar with device > > > > > > e66d8000.i2c > > > > > > > > > > > > I2C becomes available... > > > > > > > > > > > > i2c-rcar e66d8000.i2c: request_channel failed for tx (-517) > > > > > > [...] > > > > > > > > > > > > but DMA is not available yet, so the driver falls back to PIO. > > > > > > > > > > > > driver: 'i2c-rcar': driver_bound: bound to device 'e66d8000.i2c' > > > > > > bus: 'platform': really_probe: bound device e66d8000.i2c to driver i2c-rcar > > > > > > > > > > > > platform e6700000.dma-controller: Retrying from deferred list > > > > > > bus: 'platform': driver_probe_device: matched device > > > > > > e6700000.dma-controller with driver rcar-dmac > > > > > > bus: 'platform': really_probe: probing driver rcar-dmac with > > > > > > device e6700000.dma-controller > > > > > > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > > > > > > platform e6700000.dma-controller: Added to deferred list > > > > > > platform e6700000.dma-controller: Retrying from deferred list > > > > > > bus: 'platform': driver_probe_device: matched device > > > > > > e6700000.dma-controller with driver rcar-dmac > > > > > > bus: 'platform': really_probe: probing driver rcar-dmac with > > > > > > device e6700000.dma-controller > > > > > > driver: 'rcar-dmac': driver_bound: bound to device 'e6700000.dma-controller' > > > > > > bus: 'platform': really_probe: bound device > > > > > > e6700000.dma-controller to driver rcar-dmac > > > > > > > > > > > > DMA becomes available. > > > > > > > > > > > > Here userspace is entered. /sys/kernel/debug/dmaengine/summary shows > > > > > > that the I2C controllers do not have DMA channels allocated, as the > > > > > > kernel has performed no more I2C transfers after DMA became available. > > > > > > > > > > > > Using i2cdetect shows that DMA is used, which is good: > > > > > > > > > > > > i2c-rcar e66d8000.i2c: got DMA channel for rx > > > > > > > > > > > > With permissive devlinks, the clock controller consumers are not added > > > > > > to the deferred probing list, and probe order is slightly different. > > > > > > The I2C controllers are still probed before the DMA controllers. > > > > > > But DMA becomes available a bit earlier, before the probing of the last > > > > > > I2C slave driver. > > > > > > > > > > This seems like a race? I'm guessing it's two different threads > > > > > probing those two devices? And it just happens to work for > > > > > "permissive" assuming the boot timing doesn't change? > > > > > > > > > > > Hence /sys/kernel/debug/dmaengine/summary shows that > > > > > > some I2C transfers did use DMA. > > > > > > > > > > > > So the real issue is that e66d8000.i2c not linked as a consumer to > > > > > > e6700000.dma-controller. > > > > > > > > > > That's because fw_devlink.strict=1 isn't set. If you need DMA to be > > > > > treated as a mandatory supplier, you'll need to set the flag. > > > > > > > > > > Is fw_devlink=on really breaking anything here? It just seems like > > > > > "permissive" got lucky with the timing and it could break at any point > > > > > in the future. Thought? > > > > > > > > I don't think there is a race. > > > > > > Can you explain more please? This below makes it sound like DMA just > > > sneaks in at the last minute. > > > > Yes it does, as the DMAC also has a consumer link to the IOMMU. > > If you ignore the consumer link from I2C to DMAC, the I2C device has > > less dependencies than the DMAC, so the I2C device, and the > > devices on the I2C bus, are probed much earlier than the DMAC. > > Can you give this a shot? > https://lore.kernel.org/lkml/20210217235130.1744843-1-saravanak@xxxxxxxxxx/T/#u > > It should make sure fw_devlink doesn't add a device to the deferred > probe list too soon and change the probe ordering unnecessarily. (FTR, to keep all info in this thread) Yes, this makes I2C use DMA again on Salvator-XS during kernel boot-up. I haven't run any more elaborate tests on other platforms. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
