All of lore.kernel.org
 help / color / mirror / Atom feed
From: Frode Isaksen <fisaksen@baylibre.com>
To: nsekhar@ti.com, khilman@baylibre.com, ptitiano@baylibre.com,
	linux-arm-kernel@lists.infradead.org
Cc: Frode Isaksen <fisaksen@baylibre.com>,
	broonie@kernel.org, linux-spi@vger.kernel.org
Subject: [PATCH] spi: davinci: add comment about dummy tx buffer usage
Date: Fri, 17 Mar 2017 16:41:10 +0100	[thread overview]
Message-ID: <1489765270-17950-1-git-send-email-fisaksen@baylibre.com> (raw)

Add explanation about using the the rx buffer as the
dummy tx buffer.

Signed-off-by: Frode Isaksen <fisaksen@baylibre.com>
---
 drivers/spi/spi-davinci.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
index f37bbdd..595acdc 100644
--- a/drivers/spi/spi-davinci.c
+++ b/drivers/spi/spi-davinci.c
@@ -660,7 +660,11 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
 			goto err_desc;
 
 		if (!t->tx_buf) {
-			/* use rx buffer as dummy tx buffer */
+			/* To avoid errors when doing rx-only transfers with
+			 * many SG entries (> 20), use the rx buffer as the
+			 * dummy tx buffer so that dma reloads are done at the
+			 * same time for rx and tx.
+			 */
 			t->tx_sg.sgl = t->rx_sg.sgl;
 			t->tx_sg.nents = t->rx_sg.nents;
 		}
-- 
2.7.4

WARNING: multiple messages have this Message-ID (diff)
From: fisaksen@baylibre.com (Frode Isaksen)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] spi: davinci: add comment about dummy tx buffer usage
Date: Fri, 17 Mar 2017 16:41:10 +0100	[thread overview]
Message-ID: <1489765270-17950-1-git-send-email-fisaksen@baylibre.com> (raw)

Add explanation about using the the rx buffer as the
dummy tx buffer.

Signed-off-by: Frode Isaksen <fisaksen@baylibre.com>
---
 drivers/spi/spi-davinci.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
index f37bbdd..595acdc 100644
--- a/drivers/spi/spi-davinci.c
+++ b/drivers/spi/spi-davinci.c
@@ -660,7 +660,11 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
 			goto err_desc;
 
 		if (!t->tx_buf) {
-			/* use rx buffer as dummy tx buffer */
+			/* To avoid errors when doing rx-only transfers with
+			 * many SG entries (> 20), use the rx buffer as the
+			 * dummy tx buffer so that dma reloads are done at the
+			 * same time for rx and tx.
+			 */
 			t->tx_sg.sgl = t->rx_sg.sgl;
 			t->tx_sg.nents = t->rx_sg.nents;
 		}
-- 
2.7.4

             reply	other threads:[~2017-03-17 15:41 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-17 15:41 Frode Isaksen [this message]
2017-03-17 15:41 ` [PATCH] spi: davinci: add comment about dummy tx buffer usage Frode Isaksen
2017-03-17 22:01 ` Applied "spi: davinci: add comment about dummy tx buffer usage" to the spi tree Mark Brown
2017-03-17 22:01   ` Mark Brown

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1489765270-17950-1-git-send-email-fisaksen@baylibre.com \
    --to=fisaksen@baylibre.com \
    --cc=broonie@kernel.org \
    --cc=khilman@baylibre.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-spi@vger.kernel.org \
    --cc=nsekhar@ti.com \
    --cc=ptitiano@baylibre.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.