August 11, 2023 at 11:40 PM, "Dave Jiang" <dave.jiang@xxxxxxxxx> wrote:
>
> On 8/11/23 01:16, Yajun Deng wrote:
>
> >
> > The chancnt would be updated in __dma_async_device_channel_register(),
> > but it was assigned in ioat_enumerate_channels(). Therefore chancnt has
> > the wrong value.
> > Clear chancnt before calling dma_async_device_register().
> > Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx>
> >
>
> Thank you for the patch Yajun.
>
> While this may work, it clobbers the chancnt read from the hardware. I think the preferable fix is to move the value read from the hardware in ioat_enumerate_channels() and its current usages to 'struct ioatdma_device' and leave dma->chancnt unchanged in that function so that zeroing it later is not needed.
>
Yes, it's even better. I noticed that chancnt is hardware related in ioat, so I just clear it before calling dma_async_device_register().It would be updated after calling dma_async_device_register(). And it would have
the same value with read in ioat_enumerate_channels().
It doesn't seem clobber the chancnt read from the hardware.
> Also, have you tested this patch or is this just from visual inspection?
>
Yes, I tested it.
➜ ~ ls /sys/class/dma
dma0chan0 dma1chan0 dma2chan0 dma3chan0
before:
➜ ~ cat /sys/kernel/debug/dmaengine/summary
dma0 (0000:00:04.0): number of channels: 2
dma1 (0000:00:04.1): number of channels: 2
dma2 (0000:00:04.2): number of channels: 2
dma3 (0000:00:04.3): number of channels: 2
after:
➜ ~ cat /sys/kernel/debug/dmaengine/summary
dma0 (0000:00:04.0): number of channels: 1
dma1 (0000:00:04.1): number of channels: 1
dma2 (0000:00:04.2): number of channels: 1
dma3 (0000:00:04.3): number of channels: 1
> And need a fixes tag.
>
I've tried to find the commit introduced, it looks like it was introduced from the source.
The following commits are related to chancnt：
0bbd5f4e97ff ("[I/OAT]: Driver for the Intel(R) I/OAT DMA engine")
device->common.chancnt = ioatdma_read8(device, IOAT_CHANCNT_OFFSET);
e38288117c50 ("ioatdma: Remove the wrappers around read(bwl)/write(bwl) in ioatdma")
device->common.chancnt = readb(device->reg_base + IOAT_CHANCNT_OFFSET);
584ec22759c0 ("ioat: move to drivers/dma/ioat/")
move driver/dma/ioatdma.c to driver/dma/ioat/
f2427e276ffe ("ioat: split ioat_dma_probe into core/version-specific routines")
dma->chancnt = readb(device->reg_base + IOAT_CHANCNT_OFFSET);
55f878ec47e3 ("dmaengine: ioatdma: fixup ioatdma_device namings")
dma->chancnt = readb(ioat_dma->reg_base + IOAT_CHANCNT_OFFSET);
It looks very historic. I'm confused about which one to choose.
This is a bug, but it only affects /sys/kernel/debug/dmaengine/summary.
So I didn't add a fixes tag.
> >
> > ---
> > drivers/dma/ioat/init.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> > diff --git a/drivers/dma/ioat/init.c b/drivers/dma/ioat/init.c
> > index c4602bfc9c74..928fc8a83a36 100644
> > --- a/drivers/dma/ioat/init.c
> > +++ b/drivers/dma/ioat/init.c
> > @@ -536,8 +536,11 @@ static int ioat_probe(struct ioatdma_device *ioat_dma)
> > > static int ioat_register(struct ioatdma_device *ioat_dma)
> > {
> > - int err = dma_async_device_register(&ioat_dma->dma_dev);
> > + int err;
> > +
> > + ioat_dma->dma_dev.chancnt = 0;
> > > + err = dma_async_device_register(&ioat_dma->dma_dev);
> > if (err) {
> > ioat_disable_interrupts(ioat_dma);
> > dma_pool_destroy(ioat_dma->completion_pool);
> >
>
