linux-kernel - Re: [PATCH] mmc: renesas_sdhi_internal_dmac: Add MMC_CAP

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Date:   Thu, 14 Nov 2019 21:15:14 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Eugeniu Rosca <erosca@...adit-jv.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Simon Horman <horms+renesas@...ge.net.au>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Eugeniu Rosca <roscaeugeniu@...il.com>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>
Subject: Re: [PATCH] mmc: renesas_sdhi_internal_dmac: Add MMC_CAP_ERASE to
 Gen3 SoCs

Hi Ulf,

thanks again for the heads up.

> Let's first take a step back, because I don't know how the HW busy
> detection works for your controller.
> 
> I have noticed there is TMIO_STAT_CMD_BUSY bit being set for some
> variants, which seems to cause renesas_sdhi_wait_idle() to loop for a
> pre-defined number of loops/timeout. This looks scary, but I can't
> tell if it's really a problem.

That should be okay. The datasheet mentions that some registers can only
be accessed when either CBSY or SCLKDIVEN bits signal non-busyness.
renesas_sdhi_wait_idle() is for that.

> BTW, do you know what TMIO_STAT_CMD_BUSY actually is monitoring?

0: A command sequence has been completed.
1: A command sequence is being executed.

> I have also noticed that MMC_CAP_WAIT_WHILE_BUSY isn't set for any of
> the renesas/tmio variant hosts. Is that simply because the HW doesn't
> support this? Or because implementation is missing?

Good thing we use public development. I recalled we discussed this
before but I needed a search engine to find it again:

https://patchwork.kernel.org/patch/8114821/

Summary: The HW (at least since Gen2) has HW support for busy timeout
detection but I never came around to implement it (and even forgot about
it :( ). So, we still use a workqueue for it.

Kind regards,

   Wolfram


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