linux-hardening - Re: [PATCH v4 19/21] firmware: scm: Modify only the download bits in TCSR register

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Date:   Wed, 28 Jun 2023 17:20:37 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>, corbet@....net,
        agross@...nel.org, andersson@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        keescook@...omium.org, tony.luck@...el.com, gpiccoli@...lia.com,
        mathieu.poirier@...aro.org, catalin.marinas@....com,
        will@...nel.org, linus.walleij@...aro.org,
        andy.shevchenko@...il.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 19/21] firmware: scm: Modify only the download bits in
 TCSR register

On 28.06.2023 14:34, Mukesh Ojha wrote:
> CrashDump collection is based on the DLOAD bit of TCSR register.
> To retain other bits, we read the register and modify only the
> DLOAD bit as the other bits have their own significance.
> 
> Co-developed-by: Poovendhan Selvaraj <quic_poovendh@...cinc.com>
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> ---
>  drivers/firmware/qcom_scm.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index 104d86e49b97..a9ff77d16c42 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -30,6 +30,11 @@ module_param(download_mode, bool, 0);
>  #define SCM_HAS_IFACE_CLK	BIT(1)
>  #define SCM_HAS_BUS_CLK		BIT(2)
>  
> +#define QCOM_DOWNLOAD_FULLDUMP		 0x1
> +#define QCOM_DOWNLOAD_NODUMP		 0x0
> +#define QCOM_DOWNLOAD_MODE_SHIFT	   4
> +#define QCOM_DOWNLOAD_MODE_MASK		0x30
GENMASK and then FIELD_PREP below?

> +
>  struct qcom_scm {
>  	struct device *dev;
>  	struct clk *core_clk;
> @@ -440,6 +445,7 @@ static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>  static void qcom_scm_set_download_mode(bool enable)
>  {
>  	bool avail;
> +	int val;
What's wrong with initializing it in the same line as ret?

>  	int ret = 0;
>  
>  	avail = __qcom_scm_is_call_available(__scm->dev,
> @@ -448,8 +454,10 @@ static void qcom_scm_set_download_mode(bool enable)
>  	if (avail) {
>  		ret = __qcom_scm_set_dload_mode(__scm->dev, enable);
>  	} else if (__scm->dload_mode_addr) {
> -		ret = qcom_scm_io_writel(__scm->dload_mode_addr,
> -				enable ? QCOM_SCM_BOOT_SET_DLOAD_MODE : 0);
> +		val = (enable ? QCOM_DOWNLOAD_FULLDUMP : QCOM_DOWNLOAD_NODUMP);
unnecessary braces

Konrad
> +		val <<= QCOM_DOWNLOAD_MODE_SHIFT;
> +		ret = qcom_scm_io_update_field(__scm->dload_mode_addr,
> +				QCOM_DOWNLOAD_MODE_MASK, val);
>  	} else {
>  		dev_err(__scm->dev,
>  			"No available mechanism for setting download mode\n");