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

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Message-ID: <185f72b6-e6a1-3062-5f36-864973d12ec5@collabora.com>
Date:   Mon, 11 Apr 2022 10:35:45 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Ashish Mhetre <amhetre@...dia.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 4/11/22 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.