linux-kernel - Re: [PATCH 1/3] soundwire: bus: clear bus clash interrupt before the mask is enabled

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Date:   Mon, 1 Feb 2021 15:58:44 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bard Liao <yung-chuan.liao@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, rander.wang@...ux.intel.com,
        ranjani.sridharan@...ux.intel.com, hui.wang@...onical.com,
        pierre-louis.bossart@...ux.intel.com, sanyog.r.kale@...el.com,
        bard.liao@...el.com
Subject: Re: [PATCH 1/3] soundwire: bus: clear bus clash interrupt before the
 mask is enabled

On 26-01-21, 16:37, Bard Liao wrote:
> The SoundWire specification allows a Slave device to report a bus clash
> with the in-band interrupt mechanism when it detects a conflict while
> driving a bitSlot it owns. This can be a symptom of an electrical conflict
> or a programming error, and it's vital to detect reliably.
> 
> Unfortunately, on some platforms, bus clashes are randomly reported by
> Slave devices after a bus reset, with an interrupt status set even before
> the bus clash interrupt is enabled. These initial spurious interrupts are
> not relevant and should optionally be filtered out, while leaving the
> interrupt mechanism enabled to detect 'true' issues.
> 
> This patch suggests the addition of a Master level quirk to discard such
> interrupts. The quirk should in theory have been added at the Slave level,
> but since the problem was detected with different generations of Slave
> devices it's hard to point to a specific IP. The problem might also be
> board-dependent and hence dealing with a Master quirk is simpler.
> 
> Signed-off-by: Bard Liao <yung-chuan.liao@...ux.intel.com>
> Reviewed-by: Rander Wang <rander.wang@...ux.intel.com>
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> ---
>  drivers/soundwire/bus.c       | 10 ++++++++++
>  include/linux/soundwire/sdw.h |  4 ++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 6e1c988f3845..d394905936e4 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -1240,6 +1240,7 @@ static int sdw_slave_set_frequency(struct sdw_slave *slave)
>  static int sdw_initialize_slave(struct sdw_slave *slave)
>  {
>  	struct sdw_slave_prop *prop = &slave->prop;
> +	int status;
>  	int ret;
>  	u8 val;
>  
> @@ -1247,6 +1248,15 @@ static int sdw_initialize_slave(struct sdw_slave *slave)
>  	if (ret < 0)
>  		return ret;
>  
> +	if (slave->bus->prop.quirks & SDW_MASTER_QUIRKS_CLEAR_INITIAL_CLASH) {
> +		/* Clear bus clash interrupt before enabling interrupt mask */
> +		status = sdw_read_no_pm(slave, SDW_SCP_INT1);
> +		if (status & SDW_SCP_INT1_BUS_CLASH) {
> +			dev_warn(&slave->dev, "Bus clash detected before INT mask is enabled\n");
> +			sdw_write_no_pm(slave, SDW_SCP_INT1, SDW_SCP_INT1_BUS_CLASH);
> +		}
> +	}
> +
>  	/*
>  	 * Set SCP_INT1_MASK register, typically bus clash and
>  	 * implementation-defined interrupt mask. The Parity detection
> diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> index f0b01b728640..a2766c3b603d 100644
> --- a/include/linux/soundwire/sdw.h
> +++ b/include/linux/soundwire/sdw.h
> @@ -405,6 +405,7 @@ struct sdw_slave_prop {
>   * command
>   * @mclk_freq: clock reference passed to SoundWire Master, in Hz.
>   * @hw_disabled: if true, the Master is not functional, typically due to pin-mux
> + * @quirks: bitmask identifying optional behavior beyond the scope of the MIPI specification
>   */
>  struct sdw_master_prop {
>  	u32 revision;
> @@ -421,8 +422,11 @@ struct sdw_master_prop {
>  	u32 err_threshold;
>  	u32 mclk_freq;
>  	bool hw_disabled;
> +	u32 quirks;

Can we do u64 here please.. I dont know where we would end up.. but
would hate if we start running out of space ..


>  };
>  
> +#define SDW_MASTER_QUIRKS_CLEAR_INITIAL_CLASH	BIT(0)
> +
>  int sdw_master_read_prop(struct sdw_bus *bus);
>  int sdw_slave_read_prop(struct sdw_slave *slave);
>  
> -- 
> 2.17.1

-- 
~Vinod