Re: [edk2-devel][PATCH v2 0/2] Add Volatile Keyword to NvmExpress Passthru CQs

["Wu, Hao A" <hao.a.wu@intel.com>]

For the series:
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>

Will wait a couple of days before merging to see if comments from other reviewers.

Best Regards,
Hao Wu

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Oliver
> Smith-Denny
> Sent: Friday, April 28, 2023 1:36 AM
> To: devel@edk2.groups.io
> Cc: Wu, Hao A <hao.a.wu@intel.com>; Ni, Ray <ray.ni@intel.com>; Wang, Jian
> J <jian.j.wang@intel.com>; Gao, Liming <gaoliming@byosoft.com.cn>; Michael
> Kubacki <mikuback@linux.microsoft.com>; Sean Brogan
> <sean.brogan@microsoft.com>
> Subject: [edk2-devel][PATCH v2 0/2] Add Volatile Keyword to NvmExpress
> Passthru CQs
> 
> 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(-)
> 
> --
> 2.40.0
> 
> 
> 
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