linux-kernel - Re: [PATCH 11/15] tty: msm_serial: use dmaengine_prep_slave

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Message-ID: <ac79cc6f-9da2-4c09-b1d3-daa6f9baeea2@kernel.org>
Date: Fri, 19 Apr 2024 10:09:08 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>, gregkh@...uxfoundation.org
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>, linux-arm-msm@...r.kernel.org,
 Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH 11/15] tty: msm_serial: use dmaengine_prep_slave_sg()

On 19. 04. 24, 10:00, Marek Szyprowski wrote:
> On 19.04.2024 09:53, Jiri Slaby wrote:
>> On 19. 04. 24, 9:43, Jiri Slaby wrote:
>>> On 17. 04. 24, 14:45, Marek Szyprowski wrote:
>>>> I alse tried to change the "if (dma->mapped)" check in
>>>> msm_start_tx() to:
>>>>
>>>> 1. if (dma->tx_sg.length)
>>>>
>>>> 2. if (dma->tx_sg.page_link & ~SG_PAGE_LINK_MASK)
>>>>
>>>> but none of the above worked what is really strange and
>>>> incomprehensible
>>>> for me.
>>>>
>>>
>>> Aaaah, nevermind, what about this?
>>>
>>> Two bugs:
>>> 1) dma_map_sg() returns the number of mapped entries. Not zero!
>>> 2) And I forgot to zero tx_sg in case of error.
>>>
>>> --- a/drivers/tty/serial/msm_serial.c
>>> +++ b/drivers/tty/serial/msm_serial.c
>>> @@ -506,8 +506,8 @@ static int msm_handle_tx_dma(struct msm_port
>>> *msm_port, unsigned int count)
>>>           kfifo_dma_out_prepare(&tport->xmit_fifo, &dma->tx_sg, 1,
>>> count);
>>>
>>>           ret = dma_map_sg(port->dev, &dma->tx_sg, 1, dma->dir);
>>> -       if (ret)
>>> -               return ret;
>>> +       if (!ret)
>>
>> Still wrong, ret = -EIO missing in here.
> 
> "if (ret <= 0)" seems to be better here.

It returns unsigned, so I have a better patch. Will send in a second.

> Indeed this fixed the issue. I checked the code many times, but I missed
> this dma_map_sg() return value issue.

Perfect!

> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Could you test that one too :)?

thanks,
-- 
js
suse labs