Re: [PATCH V3 4/8] memory: tegra: Add Tegra210 EMC clock driver

Dmitry Osipenko
2019-05-15T15:25:23Z

15.05.2019 11:42, Joseph Lo пишет:
> On 5/15/19 1:04 AM, Dmitry Osipenko wrote:
>> 10.05.2019 11:47, Joseph Lo пишет:
>>> This is the initial patch for Tegra210 EMC clock driver, which doesn't
>>> include the support code and detail sequence for clock scaling yet.
>>>
>>> The driver is designed to support LPDDR4 SDRAM. Because of the LPDDR4
>>> devices need to do initial time training before it can be used, the
>>> firmware will help to do that at early boot stage. Then, the trained
>>> table for the rates we support will pass to the kernel via DT. So the
>>> driver can get the trained table for clock scaling support.
>>>
>>> For the higher rate support (above 800MHz), the periodic training is
>>> needed for the timing compensation. So basically, two methodologies for
>>> clock scaling are supported, one is following the clock changing
>>> sequence to update the EMC table to EMC registers and another is if the
>>> rate needs periodic training, then we will start a timer to do that
>>> periodically until it scales to the lower rate.
>>>
>>> Based on the work of Peter De Schrijver <pdeschrijver@nvidia.com>.
>>>
>>> Signed-off-by: Joseph Lo <josephl@nvidia.com>
>>> ---
>>
>> [snip]
>>
>>> +static int tegra210_emc_probe(struct platform_device *pdev)
>>> +{
>>> +    int i;
>>> +    unsigned long table_rate;
>>> +    unsigned long current_rate;
>>> +    struct device_node *np;
>>> +    struct platform_device *mc;
>>> +    struct tegra_emc *emc;
>>> +    struct clk_init_data init;
>>> +    struct clk *clk;
>>> +    struct resource *r, res;
>>> +    void *table_addr;
>>> +
>>> +    emc = devm_kzalloc(&pdev->dev, sizeof(*emc), GFP_KERNEL);
>>> +    if (!emc)
>>> +        return -ENOMEM;
>>> +
>>> +    np = of_parse_phandle(pdev->dev.of_node,
>>> "nvidia,memory-controller", 0);
>>> +    if (!np) {
>>> +        dev_err(&pdev->dev, "could not get memory controller\n");
>>> +        return -ENOENT;
>>> +    }
>>> +
>>> +    mc = of_find_device_by_node(np);
>>> +    of_node_put(np);
>>> +    if (!mc)
>>> +        return -ENOENT;
>>> +
>>> +    emc->mc = platform_get_drvdata(mc);
>>> +    if (!emc->mc)
>>> +        return -EPROBE_DEFER;
>>> +
>>> +    emc->ram_code = tegra_read_ram_code();
>>
>> emc->ram_code isn't used anywhere in the code.
>>
>> I haven't checked other fields. Please remove everything that is unused.
>
> Good catch, I missed this when clean up the code for V3.
>
>>
>>> +    r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>> +    emc->emc_base[REG_EMC] = devm_ioremap_resource(&pdev->dev, r);
>>> +    r = platform_get_resource(pdev, IORESOURCE_MEM, 1);
>>> +    emc->emc_base[REG_EMC0] = devm_ioremap_resource(&pdev->dev, r);
>>> +    r = platform_get_resource(pdev, IORESOURCE_MEM, 2);
>>> +    emc->emc_base[REG_EMC1] = devm_ioremap_resource(&pdev->dev, r);
>>
>> Use devm_platform_ioremap_resource().
>>
>>> +    for (i = 0; i < TEGRA_EMC_SRC_COUNT; i++) {
>>> +        emc_src[i] = devm_clk_get(&pdev->dev,
>>> +                        emc_src_names[i]);
>>> +        if (IS_ERR(emc_src[i])) {
>>> +            dev_err(&pdev->dev, "Can not find EMC source clock\n");
>>> +            return -ENODATA;
>>> +        }
>>> +    }
>>> +
>>> +    np = of_parse_phandle(pdev->dev.of_node, "memory-region", 0);
>>> +    if (!np) {
>>> +        dev_err(&pdev->dev, "could not find EMC table\n");
>>> +        goto emc_clk_register;
>>> +    }
>>> +
>>> +    if (!of_device_is_compatible(np, "nvidia,tegra210-emc-table") ||
>>> +        !of_device_is_available(np)) {
>>> +        dev_err(&pdev->dev, "EMC table is invalid\n");
>>> +        goto emc_clk_register;
>>> +    }
>>> +
>>> +    of_address_to_resource(np, 0, &res);
>>> +    table_addr = memremap(res.start, resource_size(&res), MEMREMAP_WB);
>>> +    of_node_put(np);
>>> +    if (!table_addr) {
>>> +        dev_err(&pdev->dev, "could not map EMC table\n");
>>> +        goto emc_clk_register;
>>> +    }
>>> +    emc->emc_table = (struct emc_table *)table_addr;
>>> +
>>> +    for (i = 0; i < TEGRA_EMC_MAX_FREQS; i++)
>>> +        if (emc->emc_table[i].rev != 0)
>>> +            emc->emc_table_size++;
>>> +        else
>>> +            break;
>>> +
>>> +    /* Init EMC rate statistic data */
>>> +    emc_stats.clkchange_count = 0;
>>> +    spin_lock_init(&emc_stats.spinlock);
>>> +    emc_stats.last_update = get_jiffies_64();
>>> +    emc_stats.last_sel = TEGRA_EMC_MAX_FREQS;
>>> +
>>> +    /* Check the supported sequence */
>>> +    while (seq->table_rev) {
>>> +        if (seq->table_rev == emc->emc_table[0].rev)
>>> +            break;
>>> +        seq++;
>>> +    }
>>> +    if (!seq->set_clock) {
>>> +        seq = NULL;
>>> +        dev_err(&pdev->dev, "Invalid EMC sequence for table Rev. %d\n",
>>> +            emc->emc_table[0].rev);
>>> +        goto emc_clk_register;
>>
>> Why do you want to register EMC clock if something fails? KMSG will be
>> flooded with errors coming from clk_set_rate.
>>
>
> See patch 7 in the series, the legacy EMC clock will be removed later,
> so we need to register the EMC clock whether the table is ready or not> In that case, I mean if the table is not available, it will still
> register EMC clock at the rate that boot loader configured before kernel
> booting. So the MC clock can still work as expected, which is under EMC
> clock.
>
> And I did test that, couldn't observe any KMSG in that case.

Looks like it kinda should work in the end.

Although it's not good that now MC driver relies on the EMC driver
presence. Maybe it's not the best variant with moving the clock stuff
into the EMC driver?

What about the backwards compatibility for DT that doesn't have the EMC
node?

What if EMC driver is disabled in the kernel's config?

And lastly.. what stops the MC driver to probe before the EMC? Looks
like MC driver is already in trouble because it's on arch level and the
EMC is on subsys, hence MC will get the orphaned clock and won't
initialize hardware properly on probe.

BTW, how are you testing the EMC driver? Is there T210 devfreq patches
in works? Or what's the user of the EMC on T210?