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Date:   Tue, 22 Mar 2022 23:34:19 +0530
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Subject: Re: [Patch v5 1/4] memory: tegra: Add memory controller channels
 support
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To:     Krzysztof Kozlowski <krzk@kernel.org>, robh+dt@kernel.org,
        thierry.reding@gmail.com, digetx@gmail.com, jonathanh@nvidia.com,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
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Cc:     vdumpa@nvidia.com, Snikam@nvidia.com
References: <20220316092525.4554-1-amhetre@nvidia.com>
 <20220316092525.4554-2-amhetre@nvidia.com>
 <81aa7be7-0bfa-05e6-624a-393e6810dc61@kernel.org>
From:   Ashish Mhetre <amhetre@nvidia.com>
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On 3/20/2022 6:01 PM, Krzysztof Kozlowski wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 16/03/2022 10:25, Ashish Mhetre wrote:
>>  From tegra186 onwards, memory controller support multiple channels.
>> Add support for mapping address spaces of these channels.
>> Make sure that number of channels are as expected on each SOC.
>> During error interrupts from memory controller, appropriate registers
>> from these channels need to be accessed for logging error info.
>>
>> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
>> ---
>>   drivers/memory/tegra/mc.c       |  6 ++++
>>   drivers/memory/tegra/tegra186.c | 52 +++++++++++++++++++++++++++++++++
>>   drivers/memory/tegra/tegra194.c |  1 +
>>   drivers/memory/tegra/tegra234.c |  1 +
>>   include/soc/tegra/mc.h          |  7 +++++
>>   5 files changed, 67 insertions(+)
>>
>> diff --git a/drivers/memory/tegra/mc.c b/drivers/memory/tegra/mc.c
>> index bf3abb6d8354..3cda1d9ad32a 100644
>> --- a/drivers/memory/tegra/mc.c
>> +++ b/drivers/memory/tegra/mc.c
>> @@ -749,6 +749,12 @@ static int tegra_mc_probe(struct platform_device *pdev)
>>        if (IS_ERR(mc->regs))
>>                return PTR_ERR(mc->regs);
>>
>> +     if (mc->soc->ops && mc->soc->ops->map_regs) {
>> +             err = mc->soc->ops->map_regs(mc, pdev);
>> +             if (err < 0)
>> +                     return err;
>> +     }
>> +
>>        mc->debugfs.root = debugfs_create_dir("mc", NULL);
>>
>>        if (mc->soc->ops && mc->soc->ops->probe) {
>> diff --git a/drivers/memory/tegra/tegra186.c b/drivers/memory/tegra/tegra186.c
>> index 3d153881abc1..a8a45e6ff1f1 100644
>> --- a/drivers/memory/tegra/tegra186.c
>> +++ b/drivers/memory/tegra/tegra186.c
>> @@ -139,11 +139,62 @@ static int tegra186_mc_probe_device(struct tegra_mc *mc, struct device *dev)
>>        return 0;
>>   }
>>
>> +static int tegra186_mc_map_regs(struct tegra_mc *mc,
>> +                             struct platform_device *pdev)
>> +{
>> +     struct device_node *np = pdev->dev.parent->of_node;
>> +     int num_dt_channels, reg_cells = 0;
>> +     struct resource *res;
>> +     int i, ret;
>> +     u32 val;
>> +
>> +     ret = of_property_read_u32(np, "#address-cells", &val);
>> +     if (ret) {
>> +             dev_err(&pdev->dev, "missing #address-cells property\n");
>> +             return ret;
>> +     }
>> +
>> +     reg_cells = val;
>> +
>> +     ret = of_property_read_u32(np, "#size-cells", &val);
>> +     if (ret) {
>> +             dev_err(&pdev->dev, "missing #size-cells property\n");
>> +             return ret;
>> +     }
>> +
>> +     reg_cells += val;
>> +
>> +     num_dt_channels = of_property_count_elems_of_size(pdev->dev.of_node, "reg",
>> +                                                       reg_cells * sizeof(u32));
>> +     /*
>> +      * On tegra186 onwards, memory controller support multiple channels.
>> +      * Apart from regular memory controller channels, there is one broadcast
>> +      * channel and one for stream-id registers.
>> +      */
>> +     if (num_dt_channels < mc->soc->num_channels + 2) {
>> +             dev_warn(&pdev->dev, "MC channels are missing, please update\n");
> 
> How did you address our previous comments about ABI break? I really do
> not see it.
> 
In v4 patch, error was returned from here and probe failed causing ABI
break. In v5, we are checking if number of reg items in DT is as
expected or not. If number of reg items are less then we are just
printing warning to update DT and returning 0. So probe won't fail and
driver will work as expected.
Also I had tested just driver patches with existing DT and it worked
fine.

> Best regards,
> Krzysztof