[PATCH v2] memory: tegra: Add support for DBB clock on Tegra264

[PATCH v2] memory: tegra: Add support for DBB clock on Tegra264

[Thierry Reding]

From: Thierry Reding <treding@nvidia.com>

The DBB clock is needed by many IP blocks in order to access system
memory via the data backbone. The memory controller and external memory
controllers are the central place where these accesses are managed, so
make sure that the clock can be controlled from the corresponding
driver.

Note that not all drivers fully register bandwidth requests, and hence
the EMC driver doesn't have enough information to know when it's safe to
switch the clock off, so for now it will be kept on permanently.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
Changes in v2:
- convert to dev_err_probe() (Krzysztof)

 drivers/memory/tegra/tegra186-emc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/memory/tegra/tegra186-emc.c b/drivers/memory/tegra/tegra186-emc.c
index dfddceecdd1a..03ebab6fbe68 100644
--- a/drivers/memory/tegra/tegra186-emc.c
+++ b/drivers/memory/tegra/tegra186-emc.c
@@ -22,6 +22,7 @@ struct tegra186_emc {
 	struct tegra_bpmp *bpmp;
 	struct device *dev;
 	struct clk *clk;
+	struct clk *clk_dbb;
 
 	struct tegra186_emc_dvfs *dvfs;
 	unsigned int num_dvfs;
@@ -328,6 +329,13 @@ static int tegra186_emc_probe(struct platform_device *pdev)
 		goto put_bpmp;
 	}
 
+	emc->clk_dbb = devm_clk_get_optional_enabled(&pdev->dev, "dbb");
+	if (IS_ERR(emc->clk_dbb)) {
+		err = dev_err_probe(&pdev->dev, PTR_ERR(emc->clk_dbb),
+				    "failed to get DBB clock\n");
+		goto put_bpmp;
+	}
+
 	platform_set_drvdata(pdev, emc);
 	emc->dev = &pdev->dev;
 
-- 
2.52.0

Re: [PATCH v2] memory: tegra: Add support for DBB clock on Tegra264

[Jon Hunter]

On 16/01/2026 12:37, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> The DBB clock is needed by many IP blocks in order to access system
> memory via the data backbone. The memory controller and external memory
> controllers are the central place where these accesses are managed, so
> make sure that the clock can be controlled from the corresponding
> driver.
> 
> Note that not all drivers fully register bandwidth requests, and hence
> the EMC driver doesn't have enough information to know when it's safe to
> switch the clock off, so for now it will be kept on permanently.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> Changes in v2:
> - convert to dev_err_probe() (Krzysztof)
> 
>   drivers/memory/tegra/tegra186-emc.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/memory/tegra/tegra186-emc.c b/drivers/memory/tegra/tegra186-emc.c
> index dfddceecdd1a..03ebab6fbe68 100644
> --- a/drivers/memory/tegra/tegra186-emc.c
> +++ b/drivers/memory/tegra/tegra186-emc.c
> @@ -22,6 +22,7 @@ struct tegra186_emc {
>   	struct tegra_bpmp *bpmp;
>   	struct device *dev;
>   	struct clk *clk;
> +	struct clk *clk_dbb;
>   
>   	struct tegra186_emc_dvfs *dvfs;
>   	unsigned int num_dvfs;
> @@ -328,6 +329,13 @@ static int tegra186_emc_probe(struct platform_device *pdev)
>   		goto put_bpmp;
>   	}
>   
> +	emc->clk_dbb = devm_clk_get_optional_enabled(&pdev->dev, "dbb");
> +	if (IS_ERR(emc->clk_dbb)) {
> +		err = dev_err_probe(&pdev->dev, PTR_ERR(emc->clk_dbb),
> +				    "failed to get DBB clock\n");
> +		goto put_bpmp;
> +	}
> +
>   	platform_set_drvdata(pdev, emc);
>   	emc->dev = &pdev->dev;
>   

Looks good to me!

Reviewed-by: Jon Hunter <jonathanh@nvidia.com>

Cheers
Jon

-- 
nvpublic

Re: [PATCH v2] memory: tegra: Add support for DBB clock on Tegra264

[Krzysztof Kozlowski]

On 16/01/2026 14:15, Jon Hunter wrote:
> 
> On 16/01/2026 12:37, Thierry Reding wrote:
>> From: Thierry Reding <treding@nvidia.com>
>>
>> The DBB clock is needed by many IP blocks in order to access system
>> memory via the data backbone. The memory controller and external memory
>> controllers are the central place where these accesses are managed, so
>> make sure that the clock can be controlled from the corresponding
>> driver.
>>
>> Note that not all drivers fully register bandwidth requests, and hence
>> the EMC driver doesn't have enough information to know when it's safe to
>> switch the clock off, so for now it will be kept on permanently.
>>
>> Signed-off-by: Thierry Reding <treding@nvidia.com>
>> ---
>> Changes in v2:
>> - convert to dev_err_probe() (Krzysztof)
>>
>>   drivers/memory/tegra/tegra186-emc.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/memory/tegra/tegra186-emc.c b/drivers/memory/tegra/tegra186-emc.c
>> index dfddceecdd1a..03ebab6fbe68 100644
>> --- a/drivers/memory/tegra/tegra186-emc.c
>> +++ b/drivers/memory/tegra/tegra186-emc.c
>> @@ -22,6 +22,7 @@ struct tegra186_emc {
>>   	struct tegra_bpmp *bpmp;
>>   	struct device *dev;
>>   	struct clk *clk;
>> +	struct clk *clk_dbb;
>>   
>>   	struct tegra186_emc_dvfs *dvfs;
>>   	unsigned int num_dvfs;
>> @@ -328,6 +329,13 @@ static int tegra186_emc_probe(struct platform_device *pdev)
>>   		goto put_bpmp;
>>   	}
>>   
>> +	emc->clk_dbb = devm_clk_get_optional_enabled(&pdev->dev, "dbb");


This looks like new clock and I don't see it in the bindings. Are you
sure this is not an undocumented ABI? In case this was asked last time,
commit msg or changelog should briefly mention it, to avoid exactly that
question.

Best regards,
Krzysztof

Re: [PATCH v2] memory: tegra: Add support for DBB clock on Tegra264

[Krzysztof Kozlowski]

On Fri, 16 Jan 2026 13:37:32 +0100, Thierry Reding wrote:
> The DBB clock is needed by many IP blocks in order to access system
> memory via the data backbone. The memory controller and external memory
> controllers are the central place where these accesses are managed, so
> make sure that the clock can be controlled from the corresponding
> driver.
> 
> Note that not all drivers fully register bandwidth requests, and hence
> the EMC driver doesn't have enough information to know when it's safe to
> switch the clock off, so for now it will be kept on permanently.
> 
> [...]

Applied, thanks!

[1/1] memory: tegra: Add support for DBB clock on Tegra264
      https://git.kernel.org/krzk/linux-mem-ctrl/c/f3ca1719b114bb3a64592de266f8ff9ce64f311b

Best regards,
-- 
Krzysztof Kozlowski <krzk@kernel.org>