Re: [PATCH 5.11 007/122] dmaengine: idxd: Fix clobbering of SWERR overflow bit on writeback

Pavel Machek
2021-04-20T20:13:12Z

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Hi!

> Current code blindly writes over the SWERR and the OVERFLOW bits. Write
> back the bits actually read instead so the driver avoids clobbering the
> OVERFLOW bit that comes after the register is read.

I believe this is incorrect. Changelog explains that we need to
preserve bits in the register...

> diff --git a/drivers/dma/idxd/irq.c b/drivers/dma/idxd/irq.c
> index a60ca11a5784..f1463fc58112 100644
> --- a/drivers/dma/idxd/irq.c
> +++ b/drivers/dma/idxd/irq.c
> @@ -124,7 +124,9 @@ static int process_misc_interrupts(struct idxd_device *idxd, u32 cause)
> for (i = 0; i < 4; i++)
> idxd->sw_err.bits[i] = ioread64(idxd->reg_base +
> IDXD_SWERR_OFFSET + i * sizeof(u64));
> - iowrite64(IDXD_SWERR_ACK, idxd->reg_base + IDXD_SWERR_OFFSET);
> +
> + iowrite64(idxd->sw_err.bits[0] & IDXD_SWERR_ACK,
> + idxd->reg_base + IDXD_SWERR_OFFSET);

...but that is not what the code does.

I suspect it should be

> + iowrite64(idxd->sw_err.bits[0] | IDXD_SWERR_ACK,
> + idxd->reg_base + IDXD_SWERR_OFFSET);

Best regards,
Pavel

--
http://www.livejournal.com/~pavelmachek

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