linux-kernel - Re: [PATCH V2 2/2] mmc: mmci: initialize pwr|clk|datactrl

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Date:   Thu, 26 Mar 2020 15:27:27 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Ludovic Barre <ludovic.barre@...com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH V2 2/2] mmc: mmci: initialize pwr|clk|datactrl_reg with
 their hardware values

On Wed, 25 Mar 2020 at 15:34, Ludovic Barre <ludovic.barre@...com> wrote:
>
> In mmci_write_pwr|clk|datactrlreg functions, if the desired value
> is equal to corresponding variable (pwr_reg|clk_reg|datactrl_reg),
> the value is not written in the register.
>
> At probe pwr|clk|datactrl_reg of mmci_host structure are initialized
> to 0 (kzalloc of mmc_alloc_host). But they does not necessarily reflect
> hardware value of these registers, if they are used while boot level.
> This is problematic, if we want to write 0 in these registers.

It could be, but I don't see that we ever needs to do that - at least
not before we have written some other non-zero values to them (through
the helper functions).

>
> This patch initializes pwr|clk|datactrl_reg variables with their
> hardware values while probing.

Hmm, so in principle this change seems quite okay, but I am hesitant
to pick it up - unless it really addresses a problem that you have
observed.

The reason is, this change may lead to avoiding to re-write the
register with the same value it got during boot - and who knows what
is best here.

Kind regards
Uffe

>
> Signed-off-by: Ludovic Barre <ludovic.barre@...com>
> ---
>  drivers/mmc/host/mmci.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> index 647567def612..f378ae18d5dc 100644
> --- a/drivers/mmc/host/mmci.c
> +++ b/drivers/mmc/host/mmci.c
> @@ -2085,6 +2085,10 @@ static int mmci_probe(struct amba_device *dev,
>         else if (plat->ocr_mask)
>                 dev_warn(mmc_dev(mmc), "Platform OCR mask is ignored\n");
>
> +       host->pwr_reg = readl_relaxed(host->base + MMCIPOWER);
> +       host->clk_reg = readl_relaxed(host->base + MMCICLOCK);
> +       host->datactrl_reg = readl_relaxed(host->base + MMCIDATACTRL);
> +
>         /* We support these capabilities. */
>         mmc->caps |= MMC_CAP_CMD23;
>
> --
> 2.17.1
>