linux-kernel - Re: [PATCH] ASoC: Intel: sst: ipc command timeout

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Date:   Tue, 14 Apr 2020 10:59:47 +0200
From:   Amadeusz Sławiński 
        <amadeuszx.slawinski@...ux.intel.com>
To:     Brent Lu <brent.lu@...el.com>, alsa-devel@...a-project.org
Cc:     Kate Stewart <kstewart@...uxfoundation.org>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Takashi Iwai <tiwai@...e.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Richard Fontana <rfontana@...hat.com>,
        Mark Brown <broonie@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>
Subject: Re: [PATCH] ASoC: Intel: sst: ipc command timeout



On 4/10/2020 10:18 AM, Brent Lu wrote:
> After sending an ipc command to DSP, the host waits for the reply message
> which will be read from SST_IPCD register in sst_byt_irq_thread() to
> complete the transaction. Sometimes the value read from SST_IPCD register
> is still the reply message for previous command instead of the waiting
> command so ipc command timeout happens.
> 
> In an experiment we read the same SST_IPCD register again when the defect
> happens and found the value of second read is different from previous one
> and is the correct reply message. It suggests the DSP is okay but the way
> we read the register may be the cause.
> 
> Currently the driver is using memcpy_fromio() to read the value of 64-bit
> registers. This function is based on __builtin_memcpy() call and depends
> on the implementation of compiler. Since this issue happens right after
> the toolchain switched from clang 10 to clang 11, we replace the register
> read with two readl() function calls to avoid all optimization from
> compiler's library.
> 
> Signed-off-by: Brent Lu <brent.lu@...el.com>
> ---
>   sound/soc/intel/common/sst-dsp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/soc/intel/common/sst-dsp.c b/sound/soc/intel/common/sst-dsp.c
> index ec66be2..12af7aa 100644
> --- a/sound/soc/intel/common/sst-dsp.c
> +++ b/sound/soc/intel/common/sst-dsp.c
> @@ -42,7 +42,7 @@ u64 sst_shim32_read64(void __iomem *addr, u32 offset)
>   {
>   	u64 val;
>   
> -	memcpy_fromio(&val, addr + offset, sizeof(val));
> +	sst_memcpy_fromio_32(NULL, &val, addr + offset, sizeof(val));
>   	return val;
>   }
>   EXPORT_SYMBOL_GPL(sst_shim32_read64);
> 

I'm not convinced that it is a correct fix. From your description it 
seems to be a timing issue and you are just masking a problem, while 
real problem is flow which allows to read data before confirming that 
DSP finished processing.