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

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Message-ID: <c3e6a50f-c098-5165-a596-ee386ac533e8@collabora.com>
Date:   Mon, 11 Apr 2022 14:13:43 +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 12:18, Ashish Mhetre wrote:
> 
> 
> 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?

Yes