linux-kernel - Re: [RFC 0/2] dw_mmc: add multislot support

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Message-ID: <CAPDyKFr4WXgFEDLGztRoSrAFMrHC7ASJxaxCTKMeGN8i-Ns86w@mail.gmail.com>
Date:   Thu, 26 Apr 2018 08:28:04 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:     "jh80.chung@...sung.com" <jh80.chung@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "krzk@...nel.org" <krzk@...nel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "kgene@...nel.org" <kgene@...nel.org>,
        "shawn.lin@...k-chips.com" <shawn.lin@...k-chips.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>
Subject: Re: [RFC 0/2] dw_mmc: add multislot support

[...]

> A bit remark for better understanding:
>
> All card settings change are serialized too. These settings are applied
> after slot switch before execution of new request for this slot.
>
> So situations like calling any host_0 ops while another host (host_1) is active
> are handled by current code.
>
> This is example of simultaneous ops calls for both slots:
>
> host (slot) 0    | host (slot) 1
> -----------------------------------
> h0->set_ios()    |    h1->set_ios()
> h0->request()    |    h1->request()
> h0->set_ios()    |    h1->set_ios()
> h0->request()    |    h1->request()
> h0->request()    |
> h0->request()    |
> h0->request()    |
>
> How it will be serialized in the mmc driver:
>
> h0->set_ios()   // h0 settings save
> h1->set_ios()   // h1 settings save
> h0->request()   // apply settings for h0 and do request

This doesn't work as it would mean violation of the specs in some
scenarios. Particular during the card initialization and card power
off.

> ------ slot switch to h1 ------
> h1->request()   // apply settings for h1 and do request

Ditto. Etc...

> h0->set_ios()   // h0 settings save
> h1->set_ios()   // h1 settings save
> ------ slot switch to h0 ------
> h0->request()   // apply settings for h0 and do request
> ------ slot switch to h1 ------
> h1->request()   // apply settings for h1 and do request
> ------ slot switch to h0 ------
> h0->request()   // do request (no new settings to apply)
> h0->request()   // do request (no new settings to apply)
> h0->request()   // do request (no new settings to apply)
>

Kind regards
Uffe