linux-kernel - Re: [PATCH v1] serial: qcom-geni: Remove alias dependency from qcom serial driver

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Message-ID: <75ebb440-f5b7-4035-a6a2-ce1280246fb4@quicinc.com>
Date: Thu, 27 Mar 2025 12:42:19 +0530
From: Viken Dadhaniya <quic_vdadhani@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
CC: <gregkh@...uxfoundation.org>, <jirislaby@...nel.org>,
        <johan+linaro@...nel.org>, <dianders@...omium.org>,
        <konradybcio@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
        <quic_msavaliy@...cinc.com>, <quic_anupkulk@...cinc.com>
Subject: Re: [PATCH v1] serial: qcom-geni: Remove alias dependency from qcom
 serial driver



On 3/4/2025 11:15 PM, Bjorn Andersson wrote:
> On Tue, Mar 04, 2025 at 12:44:23PM +0530, Viken Dadhaniya wrote:
>> Remove the dependency on aliases in the device tree configuration for the
>> qcom serial driver. Currently, the absence of an alias results in an
>> invalid line number, causing the driver probe to fail for geni serial.
>>
>> To prevent probe failures, implement logic to dynamically assign line
>> numbers if an alias is not present in the device tree for non-console
>> ports.
>>
> 
> Please read and follow https://docs.kernel.org/process/submitting-patches.html#describe-your-changes
> 
> Start with your problem description, then a description of your proposed
> solution.

Sure, Updated in v2.

> 
>> Signed-off-by: Viken Dadhaniya <quic_vdadhani@...cinc.com>
>> ---
>>   drivers/tty/serial/qcom_geni_serial.c | 26 +++++++++++++++++++++++---
>>   1 file changed, 23 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
>> index a80ce7aaf309..2457f39dfc84 100644
>> --- a/drivers/tty/serial/qcom_geni_serial.c
>> +++ b/drivers/tty/serial/qcom_geni_serial.c
>> @@ -98,6 +98,8 @@
>>   
>>   #define DMA_RX_BUF_SIZE		2048
>>   
>> +static DEFINE_IDR(port_idr);
> 
> You're just looking for a index allocator, so DEFINE_IDA() is probably
> what you want to use.
> 
> 
> That said, theoretically I think we could get 24 GENI serial instances
> in a system. Making this a huge waste of memory and CPU cycles.
> 
> An empty idr takes 88 bytes, if you then allocate 1 entry it grows with
> at least one xa_array node which is 576 bytes.

Use IDA in v2.

> 
>> +
>>   struct qcom_geni_device_data {
>>   	bool console;
>>   	enum geni_se_xfer_mode mode;
>> @@ -253,10 +255,25 @@ static struct qcom_geni_serial_port *get_port_from_line(int line, bool console)
>>   	struct qcom_geni_serial_port *port;
>>   	int nr_ports = console ? GENI_UART_CONS_PORTS : GENI_UART_PORTS;
>>   
>> -	if (line < 0 || line >= nr_ports)
>> -		return ERR_PTR(-ENXIO);
>> +	if (console) {
>> +		if (line < 0 || line >= nr_ports)
>> +			return ERR_PTR(-ENXIO);
>> +
>> +		port = &qcom_geni_console_port;
>> +	} else {
>> +		int max_alias_num = of_alias_get_highest_id("serial");
>> +
>> +		if (line < 0 || line >= nr_ports)
>> +			line = idr_alloc(&port_idr, (void *)port, max_alias_num + 1, nr_ports,
>> +					 GFP_KERNEL);
>> +		else
>> +			line = idr_alloc(&port_idr, (void *)port, line, nr_ports, GFP_KERNEL);
>> +
>> +		if (line < 0)
>> +			return ERR_PTR(-ENXIO);
>>   
>> -	port = console ? &qcom_geni_console_port : &qcom_geni_uart_ports[line];
>> +		port = &qcom_geni_uart_ports[line];
> 
> Plus qcom_geni_uart_ports[] is GENI_UART_PORTS long. So you will
> actually only have a maximum of 3 ports.
> 

Yes, that's correct. We are also working on increasing the number of 
serial ports to support more ports on GENI hardware.

> 
> I like the change, but please replace port_idr with a u32 and use
> linux/bitmap.h to implement the port allocation scheme.

As per Greg's comment, used ida in v2.

> 
> Regards,
> Bjorn
> 
>> +	}
>>   	return port;
>>   }
>>   
>> @@ -1761,6 +1778,7 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
>>   						port->wakeup_irq);
>>   		if (ret) {
>>   			device_init_wakeup(&pdev->dev, false);
>> +			idr_remove(&port_idr, uport->line);
>>   			uart_remove_one_port(drv, uport);
>>   			return ret;
>>   		}
>> @@ -1772,10 +1790,12 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
>>   static void qcom_geni_serial_remove(struct platform_device *pdev)
>>   {
>>   	struct qcom_geni_serial_port *port = platform_get_drvdata(pdev);
>> +	struct uart_port *uport = &port->uport;
>>   	struct uart_driver *drv = port->private_data.drv;
>>   
>>   	dev_pm_clear_wake_irq(&pdev->dev);
>>   	device_init_wakeup(&pdev->dev, false);
>> +	idr_remove(&port_idr, uport->line);
>>   	uart_remove_one_port(drv, &port->uport);
>>   }
>>   
>> -- 
>> 2.34.1
>>
>>