Hi Jiri,
On 16.04.2024 12:23, Jiri Slaby wrote:
> On 15. 04. 24, 23:17, Marek Szyprowski wrote:
>> On 05.04.2024 08:08, Jiri Slaby (SUSE) wrote:
>>> This is a preparatory for the serial-to-kfifo switch. kfifo understands
>>> only scatter-gatter approach, so switch to that.
>>>
>>> No functional change intended, it's just dmaengine_prep_slave_single()
>>> inline expanded.
>>>
>>> And in this case, switch from dma_map_single() to dma_map_sg() too.
>>> This
>>> needs struct msm_dma changes. I split the rx and tx parts into an
>>> union.
>>> TX is now struct scatterlist, RX remains the old good phys-virt-count
>>> triple.
>>>
>>> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@xxxxxxxxxx>
>>> Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
>>> Cc: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
>>> Cc: linux-arm-msm@xxxxxxxxxxxxxxx
>>
>> I've just found that this patch broke UART operation on DragonBoard
>> 410c. I briefly checked and didn't notice anything obviously wrong here,
>> but the board stops transmitting any data from its serial port after the
>> first message. I will try to analyze this issue a bit more tomorrow.
>
> I double checked, but I see no immediate issues in the patch too. So
> please, if you can analyze this more…
I've spent some time digging into this issue and frankly speaking I
still have no idea WHY it doesn't work (or I seriously mixed something
in the scatterlist principles). However I found a workaround to make it
working. Maybe it will help a bit guessing what happens there.
Here is a workaround:
diff --git a/drivers/tty/serial/msm_serial.c
b/drivers/tty/serial/msm_serial.c
index ae7a8e3cf467..fd3f3bf03f33 100644
--- a/drivers/tty/serial/msm_serial.c
+++ b/drivers/tty/serial/msm_serial.c
@@ -169,6 +169,7 @@ struct msm_dma {
} rx;
struct scatterlist tx_sg;
};
+ int mapped;
dma_cookie_t cookie;
u32 enable_bit;
struct dma_async_tx_descriptor *desc;
@@ -278,6 +279,7 @@ static void msm_stop_dma(struct uart_port *port,
struct msm_dma *dma)
if (dma->dir == DMA_TO_DEVICE) {
dma_unmap_sg(dev, &dma->tx_sg, 1, dma->dir);
sg_init_table(&dma->tx_sg, 1);
+ dma->mapped = 0;
} else
dma_unmap_single(dev, dma->rx.phys, mapped,
dma->dir);
}
@@ -434,7 +436,7 @@ static void msm_start_tx(struct uart_port *port)
struct msm_dma *dma = &msm_port->tx_dma;
/* Already started in DMA mode */
- if (sg_dma_len(&dma->tx_sg))
+ if (dma->mapped)
return;
msm_port->imr |= MSM_UART_IMR_TXLEV;
@@ -462,7 +464,7 @@ static void msm_complete_tx_dma(void *args)
uart_port_lock_irqsave(port, &flags);
/* Already stopped */
- if (!sg_dma_len(&dma->tx_sg))
+ if (!dma->mapped)
goto done;
dmaengine_tx_status(dma->chan, dma->cookie, &state);
@@ -481,6 +483,7 @@ static void msm_complete_tx_dma(void *args)
count = sg_dma_len(&dma->tx_sg) - state.residue;
uart_xmit_advance(port, count);
sg_init_table(&dma->tx_sg, 1);
+ dma->mapped = 0;
/* Restore "Tx FIFO below watermark" interrupt */
msm_port->imr |= MSM_UART_IMR_TXLEV;
@@ -522,6 +525,7 @@ static int msm_handle_tx_dma(struct msm_port
*msm_port, unsigned int count)
dma->desc->callback_param = msm_port;
dma->cookie = dmaengine_submit(dma->desc);
+ dma->mapped = 1;
ret = dma_submit_error(dma->cookie);
if (ret)
goto unmap;
@@ -549,6 +553,7 @@ static int msm_handle_tx_dma(struct msm_port
*msm_port, unsigned int count)
unmap:
dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
sg_init_table(&dma->tx_sg, 1);
+ dma->mapped = 0;
return ret;
}
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
