linux-kernel - Re: [PATCH v4 5/6] soc: qcom: Add LLCC support for multi channel DDR

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Date:   Fri, 30 Jun 2023 19:21:06 +0530
From:   Komal Bajaj <quic_kbajaj@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
CC:     <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v4 5/6] soc: qcom: Add LLCC support for multi channel DDR



On 6/28/2023 4:43 PM, Konrad Dybcio wrote:
> On 28.06.2023 10:52, Komal Bajaj wrote:
>>
>> On 6/23/2023 8:28 PM, Konrad Dybcio wrote:
>>> On 23.06.2023 16:18, Komal Bajaj wrote:
>>>> Add LLCC support for multi channel DDR configuration
>>>> based on a feature register. Reading DDR channel
>>>> confiuration uses nvmem framework, so select the
>>>> dependency in Kconfig. Without this, there will be
>>>> errors while building the driver with COMPILE_TEST only.
>>>>
>>>> Signed-off-by: Komal Bajaj <quic_kbajaj@...cinc.com>
>>>> ---
>>>>    drivers/soc/qcom/Kconfig     |  2 ++
>>>>    drivers/soc/qcom/llcc-qcom.c | 33 ++++++++++++++++++++++++++++++---
>>>>    2 files changed, 32 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/soc/qcom/Kconfig b/drivers/soc/qcom/Kconfig
>>>> index a491718f8064..cc9ad41c63aa 100644
>>>> --- a/drivers/soc/qcom/Kconfig
>>>> +++ b/drivers/soc/qcom/Kconfig
>>>> @@ -64,6 +64,8 @@ config QCOM_LLCC
>>>>        tristate "Qualcomm Technologies, Inc. LLCC driver"
>>>>        depends on ARCH_QCOM || COMPILE_TEST
>>>>        select REGMAP_MMIO
>>>> +    select NVMEM
>>>> +    select QCOM_SCM
>>>>        help
>>>>          Qualcomm Technologies, Inc. platform specific
>>>>          Last Level Cache Controller(LLCC) driver for platforms such as,
>>>> diff --git a/drivers/soc/qcom/llcc-qcom.c b/drivers/soc/qcom/llcc-qcom.c
>>>> index 6cf373da5df9..3c29612da1c5 100644
>>>> --- a/drivers/soc/qcom/llcc-qcom.c
>>>> +++ b/drivers/soc/qcom/llcc-qcom.c
>>>> @@ -12,6 +12,7 @@
>>>>    #include <linux/kernel.h>
>>>>    #include <linux/module.h>
>>>>    #include <linux/mutex.h>
>>>> +#include <linux/nvmem-consumer.h>
>>>>    #include <linux/of.h>
>>>>    #include <linux/of_device.h>
>>>>    #include <linux/regmap.h>
>>>> @@ -943,6 +944,19 @@ static int qcom_llcc_cfg_program(struct platform_device *pdev,
>>>>        return ret;
>>>>    }
>>>>    +static int qcom_llcc_get_cfg_index(struct platform_device *pdev, u8 *cfg_index)
>>>> +{
>>>> +    int ret;
>>>> +
>>>> +    ret = nvmem_cell_read_u8(&pdev->dev, "multi-chan-ddr", cfg_index);
>>>> +    if (ret == -ENOENT) {
>>>> +        *cfg_index = 0;
>>>> +        return 0;
>>>> +    }
>>>> +
>>>> +    return ret;
>>>> +}
>>>> +
>>>>    static int qcom_llcc_remove(struct platform_device *pdev)
>>>>    {
>>>>        /* Set the global pointer to a error code to avoid referencing it */
>>>> @@ -975,11 +989,13 @@ static int qcom_llcc_probe(struct platform_device *pdev)
>>>>        struct device *dev = &pdev->dev;
>>>>        int ret, i;
>>>>        struct platform_device *llcc_edac;
>>>> -    const struct qcom_llcc_config *cfg;
>>>> +    const struct qcom_llcc_config *cfg, *entry;
>>>>        const struct llcc_slice_config *llcc_cfg;
>>>>        u32 sz;
>>>> +    u8 cfg_index;
>>>>        u32 version;
>>>>        struct regmap *regmap;
>>>> +    u32 num_entries = 0;
>>>>          drv_data = devm_kzalloc(dev, sizeof(*drv_data), GFP_KERNEL);
>>>>        if (!drv_data) {
>>>> @@ -1040,8 +1056,19 @@ static int qcom_llcc_probe(struct platform_device *pdev)
>>>>          drv_data->version = version;
>>>>    -    llcc_cfg = cfg[0]->sct_data;
>>>> -    sz = cfg[0]->size;
>>>> +    ret = qcom_llcc_get_cfg_index(pdev, &cfg_index);
>>>> +    if (ret)
>>>> +        goto err;
>>>> +
>>>> +    for (entry = cfg; entry->sct_data; entry++, num_entries++)
>>>> +        ;
>>>> +    if (cfg_index >= num_entries || cfg_index < 0) {
>>> cfg_index is an unsigned variable, it can never be < 0
>> Okay, will remove this condition.
>>
>>>> +        ret = -EINVAL;
>>>> +        goto err;
>>>> +    }
>>>> +
>>> if (cfg_index >= entry->size)? With that, you can also keep the config
>>> entries non-0-terminated in the previous patch, saving a whole lot of RAM.
>> entry->size represents the size of sct table whereas num_entries represents the number
>> of sct tables that we can have. And by this check we are validating the value read from the
>> fuse register. Am I understanding your comment correctly?
> Oh you're right.
>
> I still see room for improvement, though.
>
> For example, you duplicate assigning need_llcc_cfg, reg_offset
> and edac_reg_offset. You can add a new struct, like "sct_config" and add
> a pointer to sct_config[] & the length of this array to qcom_llcc_config.
>
> Konrad

Okay, will follow this approach.

>
>>> Konrad
>>>> +    llcc_cfg = cfg[cfg_index].sct_data;
>>>> +    sz = cfg[cfg_index].size;
>>>>          for (i = 0; i < sz; i++)
>>>>            if (llcc_cfg[i].slice_id > drv_data->max_slices)