linux-kernel - Re: [PATCH] lightnvm: move device L2P detection to core

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Date:   Fri, 3 Aug 2018 14:43:59 +0200
From:   Matias Bjørling <mb@...htnvm.io>
To:     javier@...xlabs.com
Cc:     igor.j.konopko@...el.com, marcin.dziegielewski@...el.com,
        hans.holmberg@...xlabs.com, hlitz@...c.edu,
        youngtack.jin@...cuitblvd.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lightnvm: move device L2P detection to core

On 08/03/2018 02:40 PM, Javier Gonzalez wrote:
>> On 3 Aug 2018, at 14.37, Matias Bjørling <mb@...htnvm.io> wrote:
>>
>> On 08/03/2018 02:16 PM, Javier Gonzalez wrote:
>>>> On 3 Aug 2018, at 10.54, Matias Bjørling <mb@...htnvm.io> wrote:
>>>>
>>>> A 1.2 device is able to manage the logical to physical mapping
>>>> table internally or leave it to the host.
>>>>
>>>> A target only supports one of those approaches, and therefore must
>>>> check on initialization. Move this check to core to avoid each target
>>>> implement the check.
>>>>
>>>> Signed-off-by: Matias Bjørling <mb@...htnvm.io>
>>>> ---
>>> I see where you want to go with these changes, but the way targets are
>>> layered on top of the LightNVM subsystem does not align with it.
>>> LightNVM can support different OCSSD versions and capabilities, but that
>>> does not mean that a target (e.g., pblk) does. The way I see it, core
>>> should only check for (i) the drive to expose itself in a known revision
>>> and (ii) the reported structures to be consistent. However, specific
>>> functionality is not for core to check upo.
>>
>> Why try to initialize a target, if we already know that it is incompatible?
> 
> Yes, that is my point. But the one who knows if the targets supports
> something or not is the target, not the subsystem. Here, you are making
> an assumption knowing the pblk requires the L2P on the host, but that
> could change in the future...
> 

I don't believe it can. It is not supported by the 2.0 specification. 
1.2 is legacy.

I understand this from the perspective when checking for un-even 
configurations using the geometry. But this is a spec incompatibility, 
which I don't think the target should care about.