linux-kernel - Re: [PATCH] mmc: host: dw-mmc-rockchip: avoid logspam when cd-broken

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Message-ID: <54b24f3d-3762-abbd-5ac4-dc5728f2fe4e@arm.com>
Date:   Tue, 1 Mar 2022 12:38:17 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Jaehoon Chung <jh80.chung@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>, linux-mmc@...r.kernel.org,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: host: dw-mmc-rockchip: avoid logspam when cd-broken

On 2022-03-01 11:49, Peter Geis wrote:
> On Tue, Mar 1, 2022 at 6:23 AM Robin Murphy <robin.murphy@....com> wrote:
>>
>> On 2022-02-28 22:36, Peter Geis wrote:
>>> The dw_mmc-rockchip driver drops a large amound of logspam constantly
>>> when the cd-broken flag is enabled.
>>> Set the warning to be debug ratelimited in this case.
>>
>> Isn't this just papering over some fundamental problem with the clock?
>> If it's failing to set the expected rate for communicating with a card,
>> then presumably that's an issue for correct operation in general? The
>> fact that polling for a card makes a lot more of that communication
>> happen seems unrelated :/
> 
> Good Morning,
> 
> This only happens when a card is not inserted, so communication cannot happen.

Well, I suppose there's a philosophical question in there about whether 
shouting into the void counts as "communication", but AFAIR what the 
polling function does is power up the controller, send a command, and 
see if it gets a response.

If the clock can't be set to the proper rate for low-speed discovery, 
some or all cards may not be detected properly. Conversely if it is 
already at a slow enough rate for discovery but can't be set higher once 
a proper communication mode has been established, data transfer 
performance will be terrible. Either way, it is not OK in general for 
clk_set_rate() to fail, hence the warning. You have a clock driver problem.

Cheers,
Robin.

> I found it while lighting off the SoQuartz module.
> As it is pin compatible with the RPi CM4, and the CM4 does not have a
> card detect line, sdmmc is non functional without cd-broken.
> This led to the fun spew when there wasn't a card inserted as this
> function is called every poll tick.
> 
> Thanks,
> Peter
> 
>>
>> Robin.
>>
>>> Signed-off-by: Peter Geis <pgwipeout@...il.com>
>>> ---
>>>    drivers/mmc/host/dw_mmc-rockchip.c | 9 +++++++--
>>>    1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/dw_mmc-rockchip.c b/drivers/mmc/host/dw_mmc-rockchip.c
>>> index 95d0ec0f5f3a..d0ebf0afa42a 100644
>>> --- a/drivers/mmc/host/dw_mmc-rockchip.c
>>> +++ b/drivers/mmc/host/dw_mmc-rockchip.c
>>> @@ -50,8 +50,13 @@ static void dw_mci_rk3288_set_ios(struct dw_mci *host, struct mmc_ios *ios)
>>>                cclkin = ios->clock * RK3288_CLKGEN_DIV;
>>>
>>>        ret = clk_set_rate(host->ciu_clk, cclkin);
>>> -     if (ret)
>>> -             dev_warn(host->dev, "failed to set rate %uHz\n", ios->clock);
>>> +     if (ret) {
>>> +             /* this screams when card detection is broken */
>>> +             if (host->slot->mmc->caps & MMC_CAP_NEEDS_POLL)
>>> +                     dev_dbg_ratelimited(host->dev, "failed to set rate %uHz\n", ios->clock);
>>> +             else
>>> +                     dev_warn(host->dev, "failed to set rate %uHz\n", ios->clock);
>>> +     }
>>>
>>>        bus_hz = clk_get_rate(host->ciu_clk) / RK3288_CLKGEN_DIV;
>>>        if (bus_hz != host->bus_hz) {