linux-kernel - Re: [PATCH RFC v1 2/2] mmc: host: meson-mx-sdhc: new driver for the Amlogic Meson SDHC host

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Date:   Thu, 22 Aug 2019 15:52:24 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>, jianxin.pan@...ogic.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH RFC v1 2/2] mmc: host: meson-mx-sdhc: new driver for the
 Amlogic Meson SDHC host

On Mon, 8 Jul 2019 at 19:33, Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> WiP - only partially working - see performance numbers.
>
> Odroid-C1 eMMC (HS-200):
> Amlogic's vendor driver @ Linux 3.10:
>   7781351936 bytes (7.8 GB) copied, 134.714 s, 57.8 MB/s
> This driver:
>   7781351936 bytes (7.8 GB, 7.2 GiB) copied, 189.02 s, 41.2 MB/s
>
> EC-100 eMMC (HS MMC):
> Amlogic's vendor driver @ Linux 3.10:
>   15762194432 bytes (16 GB) copied, 422.967 s, 37.3 MB/s
> This driver:
>   15762194432 bytes (16 GB, 15 GiB) copied, 9232.65 s, 1.7 MB/s
>
> 1) Amlogic's vendor driver does some magic with the divider:
>       clk_div = input_rate / clk_ios - !(input_rate%clk_ios);
>       if (!(clk_div & 0x01)) // if even number, turn it to an odd one
>          clk_div++;
>    It's not clear to me whether what the reason behind this is, what is
>    supposed to be achieved with this?
>
> 2) The hardcoded RX clock phases are taken from the vendor driver. It
>    seems that these are only valid when fclk_div3 is used as input
>    clock (however, there are four more inputs). It's not clear to me how
>    to calculate the RX clock phases in set_ios based on the input clock
>    and the ios rate.
>
> 3) The hardware supports a timeout IRQ but the max_busy_timeout is not
>    documented anywhere.
>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>

Martin, overall this looks good to me. Once you moved from RFC to a
formal patch I will check again, of course.

There are a couple of calls to readl_poll_timeout(), for different
reasons, that I have some questions about, but we can discuss those in
the next step.

[...]

Kind regards
Uffe