linux-kernel - Re: [PATCH] firmware: imx: Skip return value check for some special SCU firmware APIs

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Date:   Wed, 25 Sep 2019 13:13:02 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Anson Huang <anson.huang@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Aisheng Dong <aisheng.dong@....com>
CC:     "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH] firmware: imx: Skip return value check for some special
 SCU firmware APIs

On 25.09.2019 13:09, Anson Huang wrote:
> The SCU firmware does NOT always have return value stored in message
> header's function element even the API has response data, those special
> APIs are defined as void function in SCU firmware, so they should be
> treated as return success always.
> 
> Signed-off-by: Anson Huang <Anson.Huang@....com>
> ---
> 	- This patch is based on the patch of https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.kernel.org%2Fpatch%2F11129553%2F&amp;data=02%7C01%7Cleonard.crestez%40nxp.com%7Cc0ced6cd07f04023977008d741a07367%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637050029712216472&amp;sdata=Ccq%2Fb2RJdMqmnL7VXrl8YhOlUwC7bWiUG%2BNmiw4OsSM%3D&amp;reserved=0
> ---
>   drivers/firmware/imx/imx-scu.c | 34 ++++++++++++++++++++++++++++++++--
>   1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/imx/imx-scu.c b/drivers/firmware/imx/imx-scu.c
> index 869be7a..ced5b12 100644
> --- a/drivers/firmware/imx/imx-scu.c
> +++ b/drivers/firmware/imx/imx-scu.c
> @@ -78,6 +78,11 @@ static int imx_sc_linux_errmap[IMX_SC_ERR_LAST] = {
>   	-EIO,	 /* IMX_SC_ERR_FAIL */
>   };
>   
> +static const struct imx_sc_rpc_msg whitelist[] = {
> +	{ .svc = IMX_SC_RPC_SVC_MISC, .func = IMX_SC_MISC_FUNC_UNIQUE_ID },
> +	{ .svc = IMX_SC_RPC_SVC_MISC, .func = IMX_SC_MISC_FUNC_GET_BUTTON_STATUS },
> +};

Until now this low level IPC code didn't treat any svc/func specially 
and this seems good.

The imx_scu_call_rpc function already has an have_resp argument and 
callers are responsible to fill it. Can't we deal with this by adding an 
additional err_ret flag passed by the caller?

We can add wrapper functions to avoid tree-wide changes for all callers.

> +
>   static struct imx_sc_ipc *imx_sc_ipc_handle;
>   
>   static inline int imx_sc_to_linux_errno(int errno)
> @@ -157,11 +162,24 @@ static int imx_scu_ipc_write(struct imx_sc_ipc *sc_ipc, void *msg)
>   	return 0;
>   }
>   
> +static bool imx_scu_call_skip_return_value_check(uint8_t svc, uint8_t func)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(whitelist); i++)
> +		if (svc == whitelist[i].svc &&
> +			func == whitelist[i].func)
> +			return true;
> +
> +	return false;
> +}
> +
>   /*
>    * RPC command/response
>    */
>   int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
>   {
> +	uint8_t saved_svc, saved_func;
>   	struct imx_sc_rpc_msg *hdr;
>   	int ret;
>   
> @@ -171,8 +189,11 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
>   	mutex_lock(&sc_ipc->lock);
>   	reinit_completion(&sc_ipc->done);
>   
> -	if (have_resp)
> +	if (have_resp) {
>   		sc_ipc->msg = msg;
> +		saved_svc = ((struct imx_sc_rpc_msg *)msg)->svc;
> +		saved_func = ((struct imx_sc_rpc_msg *)msg)->func;
> +	}
>   	sc_ipc->count = 0;
>   	ret = imx_scu_ipc_write(sc_ipc, msg);
>   	if (ret < 0) {
> @@ -190,7 +211,16 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
>   
>   		/* response status is stored in hdr->func field */
>   		hdr = msg;
> -		ret = hdr->func;
> +		/*
> +		 * Some special SCU firmware APIs do NOT have return value
> +		 * in hdr->func, but they do have response data, those special
> +		 * APIs are defined as void function in SCU firmware, so they
> +		 * should be treated as return success always.
> +		 */
> +		if (!imx_scu_call_skip_return_value_check(saved_svc, saved_func))
> +			ret = hdr->func;
> +		else
> +			ret = 0;
>   	}
>   
>   out:
>