linux-kernel - Re: [PATCH 1/3] soundwire: cadence: Don't overflow the command FIFOs

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Message-ID: <ad92df90-3a5f-91ee-59d5-23116b03264a@linux.intel.com>
Date:   Thu, 1 Dec 2022 11:49:02 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>, vkoul@...nel.org
Cc:     alsa-devel@...a-project.org, patches@...nsource.cirrus.com,
        linux-kernel@...r.kernel.org, sanyog.r.kale@...el.com,
        yung-chuan.liao@...ux.intel.com
Subject: Re: [PATCH 1/3] soundwire: cadence: Don't overflow the command FIFOs



On 12/1/22 07:48, Richard Fitzgerald wrote:
> The command FIFOs are 8 entries long, so change CDNS_MCP_CMD_LEN to 8.
> 
> CDNS_MCP_CMD_LEN was originally 32, which would lead to cdns_xfer_msg()
> writing up to 32 commands into the FIFO, so any message longer than 8
> commands would fail.

The change is correct for all instances of SoundWire on Intel platforms.
That said, maybe we should capture that the Cadence IP can handle
4/8/16/32 entries - this is a hardware configuration option.

We should also mention that so far we have not sent multiple commands so
far so the code is only broken when grouping commands.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>

> 
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> Fixes: 2f52a5177caa ("soundwire: cdns: Add cadence library")
> ---
>  drivers/soundwire/cadence_master.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
> index a1de363eba3f..27699f341f2c 100644
> --- a/drivers/soundwire/cadence_master.c
> +++ b/drivers/soundwire/cadence_master.c
> @@ -127,7 +127,8 @@ MODULE_PARM_DESC(cdns_mcp_int_mask, "Cadence MCP IntMask");
>  
>  #define CDNS_MCP_CMD_BASE			0x80
>  #define CDNS_MCP_RESP_BASE			0x80
> -#define CDNS_MCP_CMD_LEN			0x20
> +/* FIFO can hold 8 commands */
> +#define CDNS_MCP_CMD_LEN			8
>  #define CDNS_MCP_CMD_WORD_LEN			0x4
>  
>  #define CDNS_MCP_CMD_SSP_TAG			BIT(31)