linux-kernel - Re: [PATCH 0/2] Misc fixes on registering PCI NVMe CMB

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Message-ID: <150c3e85594e6256d4f3254bd4ef597612cf8428.camel@icenowy.me>
Date: Thu, 13 Feb 2025 14:05:29 +0800
From: Icenowy Zheng <uwu@...nowy.me>
To: Christoph Hellwig <hch@....de>
Cc: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>, Sagi
 Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Misc fixes on registering PCI NVMe CMB

在 2025-02-13星期四的 06:54 +0100，Christoph Hellwig写道：
> On Thu, Feb 13, 2025 at 01:04:42AM +0800, Icenowy Zheng wrote:
> > Here is a small patchset that is developed during my investigation
> > of
> > a WARNING in my boot kernel log (AMD EPYC 7K62 CPU + Intel DC D4502
> > SSD), which is because of the SSD's too-small CMB block (512KB
> > only).
> 
> Hah, that's certainly and odd CMB configuration.
> 

Sure, maybe it's just intended for a little queue. Register 0x38 value
is 0x00000004, Register 0x3c is 0x00080001, and BAR 4 is 64-bit
prefetchable memory with size=512K. I tested writing arbitary data to
the BAR 4's first few words and it correctly retains (which means they
seem to be really memory instead of registers).

I saw some mention of support CMB for submission queue in the brief of
Intel D3700/3600, maybe this applies to D450x as a successor?

BTW I am not sure about the relationship between Intel D series and P
series SSDs (only knows that D series is for dual-port redundancy), and
I have a P4511 as my boot disk (D4502 is data storage), which comes
with no CMB at all. (P4511 and D4502 shares PCI ID, but not PCI
subsystem ID).