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Date: Mon, 16 Sep 2019 16:24:17 +0200 From: Lucas Stach <l.stach@...gutronix.de> To: Philipp Puschmann <philipp.puschmann@...ix.com>, linux-kernel@...r.kernel.org Cc: linux-serial@...r.kernel.org, shawnguo@...nel.org, s.hauer@...gutronix.de, jslaby@...e.com, vkoul@...nel.org, linux-imx@....com, kernel@...gutronix.de, gregkh@...uxfoundation.org, dmaengine@...r.kernel.org, dan.j.williams@...el.com, festevam@...il.com, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH 3/4] serial: imx: adapt rx buffer and dma periods On Mi, 2019-09-11 at 16:49 +0200, Philipp Puschmann wrote: > Using only 4 DMA periods for UART RX is very few if we have a high > frequency of small transfers - like in our case using Bluetooth with many > small packets via UART - causing many dma transfers but in each only > filling a fraction of a single buffer. Such a case may lead to the > situation that DMA RX transfer is triggered but no buffer is available. > While we have addressed the dma handling already we still want to avoid > UART RX FIFO overrun. So we decrease the size of the buffers and increase > their number and the total buffer size. > > Signed-off-by: Philipp Puschmann <philipp.puschmann@...ix.com> Reasoning seems sound: Reviewed-by: Lucas Stach <l.stach@...gutronix.de> > --- > drivers/tty/serial/imx.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c > index 57d6e6ba556e..cdc51569237c 100644 > --- a/drivers/tty/serial/imx.c > +++ b/drivers/tty/serial/imx.c > @@ -1028,8 +1028,6 @@ static void imx_uart_timeout(struct timer_list *t) > } > } > > -#define RX_BUF_SIZE (PAGE_SIZE) > - > /* > * There are two kinds of RX DMA interrupts(such as in the MX6Q): > * [1] the RX DMA buffer is full. > @@ -1112,7 +1110,8 @@ static void imx_uart_dma_rx_callback(void *data) > } > > /* RX DMA buffer periods */ > -#define RX_DMA_PERIODS 4 > +#define RX_DMA_PERIODS 16 > +#define RX_BUF_SIZE (PAGE_SIZE / 4) > > static int imx_uart_start_rx_dma(struct imx_port *sport) > {
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