linux-kernel - Re: [PATCH v2 6/6] arm64: dts: qcom: ipq8074: Fix 'max-frequency' value for sdhci node

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Date:   Wed, 20 Jul 2022 13:10:26 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm@...r.kernel.org, bhupesh.linux@...il.com,
        linux-kernel@...r.kernel.org, robh@...nel.org
Subject: Re: [PATCH v2 6/6] arm64: dts: qcom: ipq8074: Fix 'max-frequency'
 value for sdhci node

Hi Ulf,


On 7/18/22 6:21 PM, Ulf Hansson wrote:
> On Mon, 18 Jul 2022 at 10:47, Bhupesh Sharma <bhupesh.sharma@...aro.org> wrote:
>>
>> On 7/1/22 4:24 AM, Bjorn Andersson wrote:
>>> On Sat 14 May 16:54 CDT 2022, Bhupesh Sharma wrote:
>>>
>>>> Since the Qualcomm sdhci-msm device-tree binding has been converted
>>>> to yaml format, 'make dtbs_check' reports issues with
>>>> 'max-frequency' value for ipq8074 sdhci node:
>>>>
>>>>    arch/arm64/boot/dts/qcom/ipq8074-hk01.dtb: mmc@...4900:
>>>>     max-frequency:0:0: 384000000 is greater than the maximum of 200000000
>>>>
>>>> Fix the same.
>>>>
>>>> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
>>>> Cc: Rob Herring <robh@...nel.org>
>>>> Signed-off-by: Bhupesh Sharma <bhupesh.sharma@...aro.org>
>>>> ---
>>>>    arch/arm64/boot/dts/qcom/ipq8074.dtsi | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm64/boot/dts/qcom/ipq8074.dtsi b/arch/arm64/boot/dts/qcom/ipq8074.dtsi
>>>> index ab2a1e7955b5..b2d71af9b419 100644
>>>> --- a/arch/arm64/boot/dts/qcom/ipq8074.dtsi
>>>> +++ b/arch/arm64/boot/dts/qcom/ipq8074.dtsi
>>>> @@ -388,7 +388,7 @@ sdhc_1: mmc@...4900 {
>>>>                                <&gcc GCC_SDCC1_APPS_CLK>,
>>>>                                <&xo>;
>>>>                       clock-names = "iface", "core", "xo";
>>>> -                    max-frequency = <384000000>;
>>>> +                    max-frequency = <200000000>;
>>> This might match the binding, but someone put 384000000 there for a
>>> reason. Perhaps the binding needs to be updated instead?
>>
>> I was waiting for getting access to ipq8074 reference manual / documentation.
>> I double-checked and it seems SDCC1 on this SoC does support a max frequency
>> of 384 MHz which is strange as the SDCC2 supports 200 MHz as max frequency
>> instead.
> 
> I guess it depends on what the property is being used for from the mmc
> host driver perspective. So, to answer the question, we probably need
> to look at the code in the host driver to best understand what to do
> here.
> 
>>
>> Also the eMMC and MMC controllers on other SoCs (i.MX etx( usually support only
>> a max frequency of 200 MHz, so may be we need an exceptional addition to the
>> binding documentation here.
>>
>> @Ulf - what's your view on updating the binding documentation here? I can
>> send a v3 accordingly.
> 
> The point with the property is to let host controllers specify whether
> there is an upper limit of the frequency that it can support. No
> matter what, the mmc core will not use a frequency greater than stated
> by the eMMC/SD/SDIO specs.
> 
> For eMMC, 200MHz is the maximum frequency.
> 
> For SD/SDIO cards, the SDR104 mode has 208MHz. So it seems like we
> need an update to the binding, no matter what. :-)
> 
> I have no strong opinions around this, but perhaps just raising the
> limit of the binding to cover the qcom case makes best sense.

Thanks for your inputs. I will send a v3 version with the udpated
binding soon.

Regards,
Bhupesh