Re: [PATCH] ath10k: fix system hang at qca99x0 probe on x86 platform

[Ben Greear <greearb@candelatech.com>]

On 06/13/2016 11:17 PM, Rajkumar Manoharan wrote:
> commit b057886524be ("ath10k: do not use coherent memory for allocated
> device memory chunks") replaced coherent memory allocation for memory
> chunks to fix low memory platforms. Unfortunately this is causing system
> freeze on x86 platform while bringing up qca99x0 device. The system
> hangs while DMA mapping bigger memory chunks (689816/865444 bytes). Fix
> this by limiting maximum memory chunk size to 256 KiB per request.
>
> Cc: Felix Fietkau <nbd@nbd.name>
> Fixes: b057886524be ("ath10k: do not use coherent memory for allocated device memory chunks")
> Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
> ---
>   drivers/net/wireless/ath/ath10k/wmi.c | 6 ++++++
>   drivers/net/wireless/ath/ath10k/wmi.h | 1 +
>   2 files changed, 7 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ath10k/wmi.c b/drivers/net/wireless/ath/ath10k/wmi.c
> index 6279ab4a760e..7c15f65fe5ed 100644
> --- a/drivers/net/wireless/ath/ath10k/wmi.c
> +++ b/drivers/net/wireless/ath/ath10k/wmi.c
> @@ -4411,6 +4411,12 @@ static int ath10k_wmi_alloc_chunk(struct ath10k *ar, u32 req_id,
>   		if (!pool_size)
>   			return -EINVAL;
>
> +		if (pool_size > WMI_MAX_MEM_CHUNK_SIZE) {
> +			num_units = WMI_MAX_MEM_CHUNK_SIZE /
> +					round_up(unit_len, 4);
> +			pool_size = num_units * round_up(unit_len, 4);
> +		}

I started testing my 9980 x86-64 system with VT/d enabled today.
With this patch in my tree, it crashes on bootup (with my firmware).
Works fine without this patch.

I don't see the exact place it is crashing in the firmware, though I could
probably narrow it down with some effort.  It is in the early startup code,
at least, which makes debugging more difficult.

This patch works fine with a slightly newer firmware compiled for 9984.  That
same firmware compiled for 9980 crashes, but I am not certain it is the same issue
as the older 9980.  It appears similar, at least.

Looks to me like there are lots of variances in how firmware and chip revisions
deal with this particular code, so we are going to have to test on lots of chips
and platforms to know if a 'fix' is really a fix or not.

Thanks,
Ben


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com