linux-kernel - Re: [PATCH v1 1/3] spi: geni-qcom: Improve target mode allocation by using proper allocation functions

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Message-ID: <d9fc3b0c-7fe7-4845-b55d-ce6d0053f48d@oss.qualcomm.com>
Date: Thu, 29 Jan 2026 12:42:25 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Praveen Talari <praveen.talari@....qualcomm.com>,
        Mark Brown <broonie@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        bjorn.andersson@....qualcomm.com, dmitry.baryshkov@....qualcomm.com
Cc: prasad.sodagudi@....qualcomm.com, mukesh.savaliya@....qualcomm.com,
        quic_vtanuku@...cinc.com, aniket.randive@....qualcomm.com,
        chandana.chiluveru@....qualcomm.com, jyothi.seerapu@....qualcomm.com
Subject: Re: [PATCH v1 1/3] spi: geni-qcom: Improve target mode allocation by
 using proper allocation functions

On 1/28/26 5:32 PM, Praveen Talari wrote:
> Hi Konrad
> 
> On 1/27/2026 6:45 PM, Konrad Dybcio wrote:
>> On 1/22/26 4:10 PM, Praveen Talari wrote:
>>> The current implementation always allocates a host controller and sets the
>>> target flag later when the "spi-slave" device tree property is present.
>>> This approach is suboptimal as it doesn't utilize the dedicated allocation
>>> functions designed for target mode.
>>>
>>> Use devm_spi_alloc_target() when "spi-slave" device tree property is
>>> present, otherwise use devm_spi_alloc_host(). This replaces the previous
>>> approach of always allocating a host controller and setting target flag
>>> later.
>>>
>>> Signed-off-by: Praveen Talari <praveen.talari@....qualcomm.com>
>>> ---
>>>   drivers/spi/spi-geni-qcom.c | 15 ++++++++-------
>>>   1 file changed, 8 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
>>> index 0e5fd9df1a8f..f5d05025b196 100644
>>> --- a/drivers/spi/spi-geni-qcom.c
>>> +++ b/drivers/spi/spi-geni-qcom.c
>>> @@ -1017,6 +1017,14 @@ static int spi_geni_probe(struct platform_device *pdev)
>>>       struct clk *clk;
>>>       struct device *dev = &pdev->dev;
>>>   +    if (device_property_read_bool(dev, "spi-slave"))
>>> +        spi = devm_spi_alloc_target(dev, sizeof(*mas));
>>> +    else
>>> +        spi = devm_spi_alloc_host(dev, sizeof(*mas));
>>> +
>>> +    if (!spi)
>>> +        return -ENOMEM;
>>> +
>>>       irq = platform_get_irq(pdev, 0);
>>>       if (irq < 0)
>>>           return irq;
>>> @@ -1033,10 +1041,6 @@ static int spi_geni_probe(struct platform_device *pdev)
>>>       if (IS_ERR(clk))
>>>           return PTR_ERR(clk);
>>>   -    spi = devm_spi_alloc_host(dev, sizeof(*mas));
>>> -    if (!spi)
>>> -        return -ENOMEM;
>>
>> Is there a reason you're moving this code to the top of the function?
> 
> When CONFIG_SPI_SLAVE is disabled, the call returns NULL; therefore, I placed this check at the start of the probe() function.
> 
> ref:
> static inline struct spi_controller *devm_spi_alloc_target(struct device *dev, unsigned int size)
> {
>     if (!IS_ENABLED(CONFIG_SPI_SLAVE))
>         return NULL;
> 
>     return __devm_spi_alloc_controller(dev, size, true);
> }

That doesn't really matter since spi is not accessed beforehand
and it'd return a NULL if it failed to allocate either way

I'm not sure this is a concern nowadays with fw_devlink and
friends, but today the allocation happens after we get a clock
reference, which could throw an eprobe_defer, which I think would
cause the memory to be de-allocated again, wasting cycles

Konrad