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

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Message-ID: <8947962f-e39e-4e96-9d1e-691e40d49349@kernel.org>
Date: Fri, 19 Apr 2024 09:43:47 +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 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)
+               goto zero_out;

         dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->tx_sg, 1,
                                                 DMA_MEM_TO_DEV,
@@ -548,6 +548,7 @@ static int msm_handle_tx_dma(struct msm_port 
*msm_port, unsigned int count)
         return 0;
  unmap:
         dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
+zero_out:
         sg_init_table(&dma->tx_sg, 1);
         return ret;
  }


thanks,
-- 
js
suse labs