linux-kernel - Re: [Patch v6 1/4] memory: tegra: Add memory controller channels support

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Message-ID: <3414a89d-bb80-ec89-3605-e435c7656321@nvidia.com>
Date:   Mon, 11 Apr 2022 14:48:28 +0530
From:   Ashish Mhetre <amhetre@...dia.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Dmitry Osipenko <digetx@...il.com>,
        krzysztof.kozlowski@...aro.org, thierry.reding@...il.com,
        jonathanh@...dia.com, robh+dt@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, krzysztof.kozlowski+dt@...aro.org
Cc:     vdumpa@...dia.com, Snikam@...dia.com
Subject: Re: [Patch v6 1/4] memory: tegra: Add memory controller channels
 support



On 4/11/2022 1:05 PM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 4/11/22 10:28, Ashish Mhetre wrote:
>>
>>
>> On 4/11/2022 12:03 PM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> On 4/11/22 09:05, Ashish Mhetre wrote:
>>>>
>>>>
>>>> On 4/10/2022 7:48 PM, Dmitry Osipenko wrote:
>>>>> External email: Use caution opening links or attachments
>>>>>
>>>>>
>>>>> 06.04.2022 08:24, Ashish Mhetre пишет:
>>>>>> +     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 memory controller DT node with MC channels\n");
>>>>>> +             return 0;
>>>>>> +     }
>>>>>> +
>>>>>> +     mc->bcast_ch_regs = devm_platform_ioremap_resource_byname(pdev,
>>>>>> "mc-broadcast");
>>>>>> +     if (IS_ERR(mc->bcast_ch_regs))
>>>>>> +             return PTR_ERR(mc->bcast_ch_regs);
>>>>>
>>>>> Looks to me that you don't need to use
>>>>> of_property_count_elems_of_size()
>>>>> and could only check the "mc-broadcast" presence to decide whether this
>>>>> is an older DT.
>>>>>
>>>> Now that we are using reg-names in new DT, yes it'd be fine to just
>>>> check mc-broadcast to decide it's a new or old DT.
>>>>
>>>>> mc->bcast_ch_regs = devm_platform_ioremap_resource_byname(pdev,
>>>>> "broadcast");
>>>>> if (IS_ERR(mc->bcast_ch_regs)) {
>>>>>            dev_warn(&pdev->dev, "Broadcast channel is missing, please
>>>>> update your
>>>>> device-tree\n");
>>>>>            return PTR_ERR(mc->bcast_ch_regs);
>>>>> }
>>>>
>>>> return 0;
>>>>
>>>> to avoid DT ABI break, right?
>>>
>>> Yes, it should be "return 0".
>>
>> But if we "return 0" from here, then what about the case when ioremap()
>> actually fails with new DT i.e. when broadcast reg is present in DT?
>> In that case error should be returned and probe should be failed, right?
> 
> You should check for the -ENOENT.

I checked __devm_ioremap_resource(), it returns -EINVAL if given
resource is not present. So should we check for -EINVAL instead?