linux-hardening - Re: [PATCH v5 15/17] firmware: scm: Modify only the download bits in TCSR register

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Message-ID: <9ab47979-e06f-475d-b1ea-239e3238b2d6@quicinc.com>
Date:   Mon, 11 Sep 2023 13:41:09 +0530
From:   Kathiravan Thirumoorthy <quic_kathirav@...cinc.com>
To:     Mukesh Ojha <quic_mojha@...cinc.com>, <corbet@....net>,
        <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.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>,
        <vigneshr@...com>, <nm@...com>, <matthias.bgg@...il.com>,
        <kgene@...nel.org>, <alim.akhtar@...sung.com>,
        <bmasney@...hat.com>, <quic_tsoni@...cinc.com>
CC:     <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-hardening@...r.kernel.org>,
        <linux-remoteproc@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-gpio@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>,
        <linux-samsung-soc@...r.kernel.org>, <kernel@...cinc.com>
Subject: Re: [PATCH v5 15/17] firmware: scm: Modify only the download bits in
 TCSR register


On 9/10/2023 1:46 AM, 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>
> ---


This change doesn't cleanly apply on next-20230911. Please rebase it.

Validated this change on IPQ9574 and IPQ5332 and system is entering into 
the download mode.

Tested-by: Kathiravan Thirumoorthy <quic_kathirav@...cinc.com> # IPQ9574 
and IPQ5332


>   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 5ea8fc4fd4e8..eda92f713019 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -5,6 +5,8 @@
>   #include <linux/platform_device.h>
>   #include <linux/init.h>
>   #include <linux/interrupt.h>
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
>   #include <linux/completion.h>
>   #include <linux/cpumask.h>
>   #include <linux/export.h>
> @@ -30,6 +32,10 @@ module_param(download_mode, bool, 0);
>   #define SCM_HAS_IFACE_CLK	BIT(1)
>   #define SCM_HAS_BUS_CLK		BIT(2)
>   
> +#define QCOM_DLOAD_MASK		GENMASK(5, 4)
> +#define QCOM_DLOAD_FULLDUMP	0x1
> +#define QCOM_DLOAD_NODUMP	0x0
> +
>   struct qcom_scm {
>   	struct device *dev;
>   	struct clk *core_clk;
> @@ -444,6 +450,7 @@ static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>   
>   static void qcom_scm_set_download_mode(bool enable)
>   {
> +	u32 val = enable ? QCOM_DLOAD_FULLDUMP : QCOM_DLOAD_NODUMP;
>   	bool avail;
>   	int ret = 0;
>   
> @@ -453,8 +460,9 @@ 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);
> +		ret = qcom_scm_io_update_field(__scm->dload_mode_addr,
> +					       QCOM_DLOAD_MASK,
> +					       FIELD_PREP(QCOM_DLOAD_MASK, val));
>   	} else {
>   		dev_err(__scm->dev,
>   			"No available mechanism for setting download mode\n");