linux-kernel - Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

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Message-ID: <a3f39ee2-cdb6-4d54-a5db-6208e435972c@quicinc.com>
Date: Tue, 10 Dec 2024 02:24:27 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Rob Clark
	<robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        "Dmitry
 Baryshkov" <dmitry.baryshkov@...aro.org>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>,
        Elliot Berman <quic_eberman@...cinc.com>,
        "Pavan
 Kondeti" <quic_pkondeti@...cinc.com>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

On 12/9/2024 8:33 PM, Konrad Dybcio wrote:
> On 9.12.2024 9:19 AM, Akhil P Oommen wrote:
>> When kernel is booted in EL2, SECVID registers are accessible to the
>> KMD. So we can use that to switch GPU's secure mode to avoid dependency
>> on Zap firmware. Also, we can't load a secure firmware without a
>> hypervisor that supports it.
>>
>> Tested following configurations on sa8775p chipset (Adreno 663 gpu):
>>
>> 1. Gunyah (No KVM) - Loads zap shader based on DT
>> 2. KVM in VHE - Skips zap shader load and programs SECVID register
>> 3. KVM in nVHE - Loads zap shader based on DT
>> 4. Kernel in EL2 with CONFIG_KVM=n - Skips zap shader load and
>> 	programs SECVID register
>>
>> For (1) and (3) configuration, this patch doesn't have any impact.
>> Driver loads secure firmware based on other existing hints.
>>
>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>> ---
> 
> [...]
> 
>> +
>> +#ifdef CONFIG_ARM64
>> +	/*
>> +	 * We can access SECVID_TRUST_CNTL register when kernel is booted in EL2 mode. So, use it
>> +	 * to switch the secure mode to avoid the dependency on zap shader.
>> +	 */
>> +	if (is_kernel_in_hyp_mode())
>> +		goto direct_switch;
> 
> So I suppose this would ideally be like hv_is_hyperv_initialized()
> but for QHEE/Gunyah, which is not going to happen, as we have
> millions of devices with old unupstreamable-ABI-Gunyah running..
> 
> This looks like the next best things then, so no objections, but..
> 
> [...]
> 
>> +	ret = a6xx_switch_secure_mode(gpu);
>> +	if (!ret)
> 
> this should definitely be a if (ret)

My bad! Thanks.

-Akhil.
> 
> Konrad