linux-kernel - Re: [PATCH] firmware: vpd: Add an interface to read VPD value

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Message-ID: <e968e478-bb48-5b05-b6c4-ae1bf77f714f@linaro.org>
Date:   Wed, 9 Oct 2019 15:05:12 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>,
        Cheng-yi Chiang <cychiang@...omium.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Tzung-Bi Shih <tzungbi@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ALSA development <alsa-devel@...a-project.org>,
        Hung-Te Lin <hungte@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sean Paul <seanpaul@...omium.org>,
        Mark Brown <broonie@...nel.org>,
        Dylan Reid <dgreid@...omium.org>,
        Tzung-Bi Shih <tzungbi@...omium.org>
Subject: Re: [PATCH] firmware: vpd: Add an interface to read VPD value



On 08/10/2019 16:14, Stephen Boyd wrote:
>> 3) As my use case does not use device tree, it is hard for ASoC
>> machine to access nvmem device. I am wondering if I can use
>> nvm_cell_lookup so machine driver can find the nvmem device using a
>> con_id. But currently the cell lookup API requires a matched device,
>> which does not fit my usage because there will be different machine
>> drivers requesting the value.
>> I think I can still workaround this by adding the lookup table in
>> machine driver. This would seem to be a bit weird because I found that
>> most lookup table is added in provider side, not consumer side. Not
>> sure if this is logically correct.
> Maybe Srini has some input here. It looks like your main concern is
> consumer to provider mapping?
> 

In non-DT setup, there are various ways to lookup nvmem provider.

1> nvmem_device_get()/put() using provider devid/name. I think you 
should be able to use this in your case.
2> nvmem_register_notifier() which notifies when nvmem provider is added 
to system.
3> nvmem_device_find() with own match function this will be merged in 
next window (https://lkml.org/lkml/2019/10/3/215)


If none of these are of any help, could explain what exactly are you 
looking for w.r.t nvmem to be able to move to what Stephen Boyd suggested?

--srini