linux-kernel - Re: [PATCH] mmc: sdhci-msm: Slot indexing for distinguishing multiple SDCC instances

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Message-ID: <0a0647aa-1fa4-4149-a76d-da7e08034fe4@quicinc.com>
Date: Mon, 28 Oct 2024 16:10:37 +0530
From: Sachin Gupta <quic_sachgupt@...cinc.com>
To: Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson
	<ulf.hansson@...aro.org>
CC: <linux-arm-msm@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_cang@...cinc.com>,
        <quic_nguyenb@...cinc.com>, <quic_bhaskarv@...cinc.com>,
        <quic_mapa@...cinc.com>, <quic_narepall@...cinc.com>,
        <quic_nitirawa@...cinc.com>, <quic_rampraka@...cinc.com>,
        <quic_sartgarg@...cinc.com>
Subject: Re: [PATCH] mmc: sdhci-msm: Slot indexing for distinguishing multiple
 SDCC instances



On 10/25/2024 6:03 PM, Adrian Hunter wrote:
> On 25/10/24 13:37, Sachin Gupta wrote:
>>
>>
>> On 10/24/2024 4:38 PM, Adrian Hunter wrote:
>>> On 22/10/24 17:18, Sachin Gupta wrote:
>>>> This update addresses the requirement for accurate slot indexing
>>>> in the sdhci-msm driver to differentiate between multiple SDCC
>>>> (Secure Digital Card Controller) instances, such as eMMC, SD card,
>>>> and SDIO.
>>>>
>>>> Additionally, it revises the slot indexing logic to comply with
>>>> the new device tree (DT) specifications.
>>>
>>> This patch seems incomplete because all it does is assign a global
>>> variable which is never used again.
>>>
>>
>> Qualcomm internal debugging tools utilize this global variable to
>> access and differentiate between all the instance's sdhci_msm_host
>> data structure (eMMC, SD card, and SDIO).
> 
> The kernel does not accept code that does not serve a functional
> purpose.
> 
> You could look at using eBPF or KGDB to get the information,
> otherwise you might just have to carry that kind of patch in
> your internal tree.
> 

Sorry for misleading sentence, the tool I use is lauterbach Trace32 and 
when using Lauterbach Trace32 tool, having a global variable makes it 
easier to load and inspect dumps. It will be easy to quickly locate and 
analyze the sdhci_msm_host structure, which speeds up the debugging process.

>>
>>>>
>>>> Signed-off-by: Ram Prakash Gupta <quic_rampraka@...cinc.com>
>>>> Signed-off-by: Sarthak Garg <quic_sartgarg@...cinc.com>
>>>> Signed-off-by: Maramaina Naresh <quic_mnaresh@...cinc.com>
>>>> Signed-off-by: Ziqi Chen <quic_ziqichen@...cinc.com>
>>>> Signed-off-by: Sachin Gupta <quic_sachgupt@...cinc.com>
>>>> ---
>>>>    drivers/mmc/host/sdhci-msm.c | 10 ++++++++++
>>>>    1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
>>>> index e113b99a3eab..3cb79117916f 100644
>>>> --- a/drivers/mmc/host/sdhci-msm.c
>>>> +++ b/drivers/mmc/host/sdhci-msm.c
>>>> @@ -292,6 +292,8 @@ struct sdhci_msm_host {
>>>>        bool vqmmc_enabled;
>>>>    };
>>>>    +static struct sdhci_msm_host *sdhci_slot[3];
>>>> +
>>>>    static const struct sdhci_msm_offset *sdhci_priv_msm_offset(struct sdhci_host *host)
>>>>    {
>>>>        struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>>> @@ -2426,6 +2428,14 @@ static int sdhci_msm_probe(struct platform_device *pdev)
>>>>        if (ret)
>>>>            goto pltfm_free;
>>>>    +    if (node) {
>>>> +        ret = of_alias_get_id(pdev->dev.of_node, "mmc");
>>>> +        if (ret < 0)
>>>> +            dev_err(&pdev->dev, "get slot index failed %d\n", ret);
>>>> +        else
>>>> +            sdhci_slot[ret] = msm_host;
>>>> +    }
>>>> +
>>>>        /*
>>>>         * Based on the compatible string, load the required msm host info from
>>>>         * the data associated with the version info.
>>>
>>
>