UART DMA takes too long time to complete

Gangadhar Gangu

Hi All,

I back ported 8250 OMAP UART driver from linux3.19 to linux3.12 using http://processors.wiki.ti.com/index.php/Sitara_Linux_SDK_UART_-_Switching_to_8250_Driver . But UART DMA takes too long time to complete, around 30 secs. It's independent of data length. I've tried from 4 to 4095 bytes. Did anybody face this issue and have a solution for this?

Regards,

Gangadhar

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Forwarding this to the SW team.

0 Yordan Kovachev over 10 years ago in reply to Biser Gatchev-XID

TI__Guru**** 161600 points

Hi Gangadhar,

I haven't encountered this. Can you please give a little more details. Which board are you using? What do you use the UART for (my guess is communication with other device, right?), can you provide some pointers to replicate your problem on beagleboard?

Have you tried switching back to the omap-serial driver? Is this issue still present?

Best Regards,
Yordan

0 Gangadhar Gangu over 10 years ago in reply to Yordan Kovachev

Expert 1865 points

Hi Yordan,

I've attached the complete patch (Changes done to backport). I'm using a custom board similar to AM335x EVM. I use the UART to connect to BT chip. I probed TX line for data length greater than 3bytes for which DMA will be used, the data is wrong on TX line. I also put some debug prints and found only alloc/dealloc channel calls in 8250_dma.c file gets called and no other DMA related functions are called. I even put debug prints in "arch/arm/plat-omap/dma.c", start and stop dma functions are not called. I was using omap-serial driver, as this didn't have DMA support, I'm back porting 8250 omap driver from linux3.19 to linux3.12.0001-linux-Added-DMA-support-to-UART-driver.patch.txt

Regards,

Gangadhar

0 Yordan Kovachev over 10 years ago in reply to Gangadhar Gangu

TI__Guru**** 161600 points

Hi Gangadhar,

Could you check the following wiki: processors.wiki.ti.com/.../Sitara_Linux_UART_-_Switching_to_8250_Driver

I think you may be missing something in your kernel configuration.

Best Regards,
Yordan

0 Gangadhar Gangu over 10 years ago in reply to Yordan Kovachev

Expert 1865 points

Hi Yordan,
I've used this wiki. As suggested, I had done below configurations. I had also enabled 8250 DMA support.
Support for OMAP internal UART (8250 based driver) - Enable
OMAP serial port support - Disable

Regards,
Gangadhar

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UART DMA takes too long time to complete