linux-kernel - Re: [PATCH v6 4/4] mmc: mediatek: Add subsys clock control for MT8192 msdc

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Message-ID: <8bcc800b-fa1a-a42c-9fb7-a7546e889694@gmail.com>
Date:   Wed, 14 Oct 2020 09:44:37 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Nicolas Boichat <drinkcat@...omium.org>,
        Wenbin Mei <wenbin.mei@...iatek.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Chaotian Jing <chaotian.jing@...iatek.com>,
        linux-mmc@...r.kernel.org,
        Devicetree List <devicetree@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>
Subject: Re: [PATCH v6 4/4] mmc: mediatek: Add subsys clock control for MT8192
 msdc



On 14/10/2020 05:06, Nicolas Boichat wrote:
> On Wed, Oct 14, 2020 at 10:29 AM Wenbin Mei <wenbin.mei@...iatek.com> wrote:
>>
>> On Tue, 2020-10-13 at 17:10 +0200, Matthias Brugger wrote:
>>>
>>> On 12/10/2020 14:45, Wenbin Mei wrote:
>>>> MT8192 msdc is an independent sub system, we need control more bus
>>>> clocks for it.
>>>> Add support for the additional subsys clocks to allow it to be
>>>> configured appropriately.
>>>>
>>>> Signed-off-by: Wenbin Mei <wenbin.mei@...iatek.com>
>>>> ---
>>>>    drivers/mmc/host/mtk-sd.c | 74 +++++++++++++++++++++++++++++----------
>>>>    1 file changed, 56 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
>>>> index a704745e5882..c7df7510f120 100644
>>>> --- a/drivers/mmc/host/mtk-sd.c
>>>> +++ b/drivers/mmc/host/mtk-sd.c
>>> [...]
>>>> +static int msdc_of_clock_parse(struct platform_device *pdev,
>>>> +                          struct msdc_host *host)
>>>> +{
>>>> +   int ret;
>>>> +
>>>> +   host->src_clk = devm_clk_get(&pdev->dev, "source");
>>>> +   if (IS_ERR(host->src_clk))
>>>> +           return PTR_ERR(host->src_clk);
>>>> +
>>>> +   host->h_clk = devm_clk_get(&pdev->dev, "hclk");
>>>> +   if (IS_ERR(host->h_clk))
>>>> +           return PTR_ERR(host->h_clk);
>>>> +
>>>> +   host->bus_clk = devm_clk_get_optional(&pdev->dev, "bus_clk");
>>>> +   if (IS_ERR(host->bus_clk))
>>>> +           host->bus_clk = NULL;
>>>> +
>>>> +   /*source clock control gate is optional clock*/
>>>> +   host->src_clk_cg = devm_clk_get_optional(&pdev->dev, "source_cg");
>>>> +   if (IS_ERR(host->src_clk_cg))
>>>> +           host->src_clk_cg = NULL;
>>>> +
>>>> +   host->sys_clk_cg = devm_clk_get_optional(&pdev->dev, "sys_cg");
>>>> +   if (IS_ERR(host->sys_clk_cg))
>>>> +           host->sys_clk_cg = NULL;
>>>> +
>>>> +   /* If present, always enable for this clock gate */
>>>> +   clk_prepare_enable(host->sys_clk_cg);
>>>> +
>>>> +   host->bulk_clks[0].id = "pclk_cg";
>>>> +   host->bulk_clks[1].id = "axi_cg";
>>>> +   host->bulk_clks[2].id = "ahb_cg";
>>>
>>> That looks at least suspicious. The pointers of id point to some strings defined
>>> in the function. Aren't they out of scope once msdc_of_clock_parse() has returned?
>>>
>> These constants are not in stack range, so they will not be lost.
>> And I have confirmed it after msdc_of_clock_parse() has returned, these
>> ids still exist.
> 
> Yes I guess the constants end up in .rodata (or similar section), but
> I'm not sure if this is absolutely guaranteed.
> 
> In any case, this is a commonly used pattern, so I'd hope it's fine
> (just a sample, there are more):
> https://elixir.bootlin.com/linux/latest/source/drivers/pci/controller/dwc/pcie-qcom.c#L266
> https://elixir.bootlin.com/linux/latest/source/sound/soc/codecs/wm8994.c#L4638
> https://elixir.bootlin.com/linux/latest/source/drivers/mfd/madera-core.c#L467
> https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpio-dwapb.c#L675
> 

Alright, then this looks good, sorry for the noise!
Matthias