regression: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support") drops data

Hi Ivan,

It appears that I have found a regression caused by 3a878c430fd6 ("tty: serial: msm: Add TX DMA support").

When I cat a file slightly larger than 126000 bytes on the console, viewed via minicom connected to the serial port, I am losing random chunks of data, almost always three bytes in length. I have also seen a lost chunk of two bytes.

I am using the 8074 dragonboard, with the dts of arch/arm/boot/dts/qcom-apq8074-dragonboard.dts. The dts node is serial@f991e000, which has a compatible of "qcom,msm-uartdm-v1.4", so is_uartdm should be UARTDM_1P4.

Quoted 14 lines · Frank Rowand

Hi Ivan,

It appears that I have found a regression caused by 3a878c430fd6 ("tty: serial: msm: Add TX DMA support").

When I cat a file slightly larger than 126000 bytes on the console, viewed via minicom connected to the serial port, I am losing random chunks of data, almost always three bytes in length. I have also seen a lost chunk of two bytes.

Quoted 5 lines

I am using the 8074 dragonboard, with the dts of arch/arm/boot/dts/qcom-apq8074-dragonboard.dts. The dts node is serial@f991e000, which has a compatible of "qcom,msm-uartdm-v1.4", so is_uartdm should be UARTDM_1P4.

I don’t remember what was biggest chunk, which DMA could carry, sorry. Are you using DMA or just PIO? Is this happening only with cat and terminal or even when you send data in other means. I believe that people from Linaro could help you better.

Quoted 20 lines · Ivan Ivanov

Quoted 14 lines · Frank Rowand

Hi Ivan,

It appears that I have found a regression caused by 3a878c430fd6 ("tty: serial: msm: Add TX DMA support").

When I cat a file slightly larger than 126000 bytes on the console, viewed via minicom connected to the serial port, I am losing random chunks of data, almost always three bytes in length. I have also seen a lost chunk of two bytes.

Quoted 5 lines

I am using the 8074 dragonboard, with the dts of arch/arm/boot/dts/qcom-apq8074-dragonboard.dts. The dts node is serial@f991e000, which has a compatible of "qcom,msm-uartdm-v1.4", so is_uartdm should be UARTDM_1P4.

Quoted 5 lines

I don’t remember what was biggest chunk, which DMA could carry, sorry. Are you using DMA or just PIO? Is this happening only with cat and terminal or even when you send data in other means. I believe that people from Linaro could help you better.

I assumed you would be the person who would have the information and would be able to help maintain the code in question since you submitted this not small patch. Do you have a pointer to the hardware documentation of the DMA and uart? Who at Linaro are you suggesting?

Thanks for the questions, I'll look into them today.

One more observation that may provide an insight:
if I cat a file multiple times, the location of the dropped chunks varies.

In further testing I also found examples of single bytes lost.

Thanks,

Frank

Quoted 27 lines · Frank Rowand

Quoted 20 lines · Ivan Ivanov

Quoted 14 lines · Frank Rowand

Hi Ivan,

It appears that I have found a regression caused by 3a878c430fd6 ("tty: serial: msm: Add TX DMA support").

When I cat a file slightly larger than 126000 bytes on the console, viewed via minicom connected to the serial port, I am losing random chunks of data, almost always three bytes in length. I have also seen a lost chunk of two bytes.

Quoted 5 lines

I am using the 8074 dragonboard, with the dts of arch/arm/boot/dts/qcom-apq8074-dragonboard.dts. The dts node is serial@f991e000, which has a compatible of "qcom,msm-uartdm-v1.4", so is_uartdm should be UARTDM_1P4.

Quoted 5 lines

I don’t remember what was biggest chunk, which DMA could carry, sorry. Are you using DMA or just PIO? Is this happening only with cat and terminal or even when you send data in other means. I believe that people from Linaro could help you better.

Quoted 8 lines

I assumed you would be the person who would have the information and would be able to help maintain the code in question since you submitted this not small patch. Do you have a pointer to the hardware documentation of the DMA and uart? Who at Linaro are you suggesting?

Thanks for the questions, I'll look into them today.

I switched from cat to several variations of dd and on the host side I tried using programs other than minicom.

My symptoms have now changed to something else that I have seen in the past, but I am now suspicious of my environment. I'll reset and do some more tests.

I'm not sure if the driver was in DMA or PIO mode, both before the change and after. This seems like a rather important question to answer, so I'll try to verify that tonight.

Quoted 7 lines

One more observation that may provide an insight:
if I cat a file multiple times, the location of the dropped chunks varies.

In further testing I also found examples of single bytes lost.

Quoted 1 line · Frank Rowand

On 4/20/2016 9:48 AM, Frank Rowand wrote:

Quoted 4 lines

I'm not sure if the driver was in DMA or PIO mode, both before the change and after. This seems like a rather important question to answer, so I'll try to verify that tonight.