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Date: Thu, 4 May 2023 21:51:43 -0400
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Subject: Re: [edk2-devel][PATCH v2 0/2] Add Volatile Keyword to NvmExpress Passthru CQs
To: devel@edk2.groups.io, osde@linux.microsoft.com
Cc: Hao A Wu <hao.a.wu@intel.com>, Ray Ni <ray.ni@intel.com>,
 Jian J Wang <jian.j.wang@intel.com>, Liming Gao <gaoliming@byosoft.com.cn>,
 Sean Brogan <sean.brogan@microsoft.com>
References: <20230427173622.10614-1-osde@linux.microsoft.com>
From: "Michael Kubacki" <mikuback@linux.microsoft.com>
In-Reply-To: <20230427173622.10614-1-osde@linux.microsoft.com>
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For the series:

Acked-by: Michael Kubacki <michael.kubacki@microsoft.com>

On 4/27/2023 1:36 PM, Oliver Smith-Denny wrote:
> NVMe CQs are hardware queues mapped to EFI memory.
> In the NVMExpress Passthru implementations in PEI and DXE,
> it has been observed that NVMe CQs are not marked
> volatile, meaning the compiler has significant leeway
> to optimize accesses to these structures.
> 
> This led to an issue where the passthru driver waited
> for a timeout period for an NVMe CQ to mark that it was
> finished with a transaction, but the compiler had
> optimized away the read to the actual HW mapped memory,
> so the transaction had completed but the timeout continued.
> 
> Marking the CQs as volatile fixes this issue as the reads
> happen to the actual HW.
> 
> Personal GitHub PR: https://github.com/tianocore/edk2/pull/4320
> Github branch: https://github.com/os-d/edk2/tree/osde/volatile_cq_v2
> 
> Changes v1 => v2:
> =================
> - Remove volatile keyword from SQ
> 
> Cc: Hao A Wu <hao.a.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Michael Kubacki <mikuback@linux.microsoft.com>
> Cc: Sean Brogan <sean.brogan@microsoft.com>
> 
> 
> Oliver Smith-Denny (2):
>    Add the volatile keyword to NvmExpressDxe's Passthru CQ
>    Add volatile keyword to NvmExpressPei's Passthru CQ
> 
>   MdeModulePkg/Bus/Pci/NvmExpressDxe/NvmExpressPassthru.c    | 6 +++---
>   MdeModulePkg/Bus/Pci/NvmExpressPei/NvmExpressPeiPassThru.c | 6 +++---
>   2 files changed, 6 insertions(+), 6 deletions(-)
>