Re: [PATCH V5 5/5] firmware: scm: Modify only the DLOAD bit in TCSR register for download mode

[Sricharan Ramabadhran <quic_srichara@quicinc.com>]

<..>

>>>>>>       };
>>>>>> -    desc.args[1] = enable ? QCOM_SCM_BOOT_SET_DLOAD_MODE : 0;
>>>>>> +    desc.args[1] = enable ? val | QCOM_SCM_BOOT_SET_DLOAD_MODE :
>>>>>> +                val & ~(QCOM_SCM_BOOT_SET_DLOAD_MODE);
>>>>>>       return qcom_scm_call_atomic(__scm->dev, &desc, NULL);
>>>>>>   }
>>>>>> @@ -426,15 +427,25 @@ static void qcom_scm_set_download_mode(bool 
>>>>>> enable)
>>>>>>   {
>>>>>>       bool avail;
>>>>>>       int ret = 0;
>>>>>> +    u32 dload_addr_val;
>>>>>>       avail = __qcom_scm_is_call_available(__scm->dev,
>>>>>>                            QCOM_SCM_SVC_BOOT,
>>>>>>                            QCOM_SCM_BOOT_SET_DLOAD_MODE);
>>>>>> +    ret = qcom_scm_io_readl(__scm->dload_mode_addr, 
>>>>>> &dload_addr_val);
>>>>>> +
>>>>>> +    if (ret) {
>>>>>> +        dev_err(__scm->dev,
>>>>>> +            "failed to read dload mode address value: %d\n", ret);
>>>>>> +        return;
>>>>>> +    }
>>>>>> +
>>>>>>       if (avail) {
>>>>>> -        ret = __qcom_scm_set_dload_mode(__scm->dev, enable);
>>>>>> +        ret = __qcom_scm_set_dload_mode(__scm->dev, 
>>>>>> dload_addr_val, enable);
>>>>>
>>>>> Did you test this on a target where it comes under this if 
>>>>> statement? does it really need to know dload_mode_addr for this 
>>>>> target ?
>>>>
>>>>
>>>> Can we do something like this? I would let other review as well.
>>>>
>>>> --------------------------------------->0------------------------------------------- 
>>>>
>>>> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
>>>> index cdbfe54..26b7eda 100644
>>>> --- a/drivers/firmware/qcom_scm.c
>>>> +++ b/drivers/firmware/qcom_scm.c
>>>> @@ -419,6 +419,7 @@ static void qcom_scm_set_download_mode(bool enable)
>>>>  {
>>>>         bool avail;
>>>>         int ret = 0;
>>>> +       u32 dload_addr_val;
>>>>
>>>>         avail = __qcom_scm_is_call_available(__scm->dev,
>>>>                                              QCOM_SCM_SVC_BOOT,
>>>> @@ -426,8 +427,16 @@ 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_readl(__scm->dload_mode_addr, 
>>>> &dload_addr_val);
>>>> +               if (ret) {
>>>> +                       dev_err(__scm->dev,
>>>> +                               "failed to read dload mode address 
>>>> value: %d\n", ret);
>>>> +                       return;
>>>> +               }
>>>> +
>>>> +               ret = qcom_scm_io_writel(__scm->dload_mode_addr, 
>>>> enable ?
>>>> +                               dload_addr_val | 
>>>> QCOM_SCM_BOOT_SET_DLOAD_MODE :
>>>> +                               dload_addr_val & 
>>>> ~(QCOM_SCM_BOOT_SET_DLOAD_MODE));
>>>>         } else {
>>>>                 dev_err(__scm->dev,
>>>>                         "No available mechanism for setting download 
>>>> mode\n");
>>>>
>>>> -Mukesh
>>>
>>> Okay sure..Agreed, will address this in the next patch.
>>
>>    Also, not sure, if its better to keep the old behavior working for
>>    targets that does not support 'READ' of this address. If one such
>>    thing exists, that will be broken now. In such a case, we should
>>    ignore if scm_io_readl fails, still write and dload_addr_val should
>>    be '0' initialised.
> 
> Why would a secure read of this register would fail, if one is allowed 
> to do secure write ?
> 
> Honestly, i was not understanding the purpose of this bitwise handling
> of this patch, i thought it is trying to fix existing issue for
> some target.
> 
> For some of the upstream target(e.g sm8450, i verified it myself), it is 
> not an issue.
> 
> arch/arm64/boot/dts/qcom/msm8916.dtsi:                  qcom,dload-mode 
> = <&tcsr 0x6100>;
> arch/arm64/boot/dts/qcom/msm8976.dtsi:                  qcom,dload-mode 
> = <&tcsr 0x6100>;
> arch/arm64/boot/dts/qcom/msm8996.dtsi:                  qcom,dload-mode 
> = <&tcsr_2 0x13000>;
> arch/arm64/boot/dts/qcom/sm8450.dtsi:                   qcom,dload-mode 
> = <&tcsr 0x13000>;
> 
> 
> However, it looks valid to handle only the effective bits. I have worked 
> on top of this patch and tested it and posted here.
> 
> https://lore.kernel.org/lkml/1676990381-18184-1-git-send-email-quic_mojha@quicinc.com/ 
> 
> 
> Do you have any example of any upstream target where this would fail ?

   Actually not sure. I was saying just based on the fact that,
   previously it was 'unconditional write' on all targets, now its a
   'conditional write'. If 'read' would never fail from secure,
   then your patch looks fine.

Regards,
  Sricharan
  y



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