From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Vinod Koul <vkoul@kernel.org>, Viresh Kumar <vireshk@kernel.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>
Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru>,
Serge Semin <fancer.lancer@gmail.com>,
Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
<linux-mips@vger.kernel.org>, <devicetree@vger.kernel.org>,
<dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH v4 11/11] dmaengine: dw: Initialize max_sg_nents capability
Date: Fri, 29 May 2020 01:24:01 +0300 [thread overview]
Message-ID: <20200528222401.26941-12-Sergey.Semin@baikalelectronics.ru> (raw)
In-Reply-To: <20200528222401.26941-1-Sergey.Semin@baikalelectronics.ru>
Multi-block support provides a way to map the kernel-specific SG-table so
the DW DMA device would handle it as a whole instead of handling the
SG-list items or so called LLP block items one by one. So if true LLP
list isn't supported by the DW DMA engine, then soft-LLP mode will be
utilized to load and execute each LLP-block one by one. The soft-LLP mode
of the DMA transactions execution might not work well for some DMA
consumers like SPI due to its Tx and Rx buffers inter-dependency. Let's
initialize the max_sg_nents DMA channels capability based on the nollp
flag state. If it's true, no hardware accelerated LLP is available and
max_sg_nents should be set with 1, which means that the DMA engine
can handle only a single SG list entry at a time. If noLLP is set to
false, then hardware accelerated LLP is supported and the DMA engine
can handle infinite number of SG entries in a single DMA transaction.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
---
Changelog v3:
- This is a new patch created as a result of the discussion with Vinud and
Andy in the framework of DW DMA burst and LLP capabilities.
Changelog v4:
- Use explicit if-else statement when assigning the max_sg_nents field.
---
drivers/dma/dw/core.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 60ef779fc5e0..b76eee75fde8 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1059,6 +1059,18 @@ static void dwc_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
caps->max_burst = dwc->max_burst;
+
+ /*
+ * It might be crucial for some devices to have the hardware
+ * accelerated multi-block transfers supported, aka LLPs in DW DMAC
+ * notation. So if LLPs are supported then max_sg_nents is set to
+ * zero which means unlimited number of SG entries can be handled in a
+ * single DMA transaction, otherwise it's just one SG entry.
+ */
+ if (dwc->nollp)
+ caps->max_sg_nents = 1;
+ else
+ caps->max_sg_nents = 0;
}
int do_dma_probe(struct dw_dma_chip *chip)
--
2.26.2
next prev parent reply other threads:[~2020-05-28 22:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 22:23 [PATCH v4 00/11] dmaengine: dw: Take Baikal-T1 SoC DW DMAC peculiarities into account Serge Semin
2020-05-28 22:23 ` [PATCH v4 01/11] dt-bindings: dma: dw: Convert DW DMAC to DT binding Serge Semin
2020-05-28 22:23 ` [PATCH v4 02/11] dt-bindings: dma: dw: Add max burst transaction length property Serge Semin
2020-05-28 22:23 ` [PATCH v4 03/11] dmaengine: Introduce min burst length capability Serge Semin
2020-05-29 12:07 ` Andy Shevchenko
2020-05-28 22:23 ` [PATCH v4 04/11] dmaengine: Introduce max SG list entries capability Serge Semin
2020-05-28 22:23 ` [PATCH v4 05/11] dmaengine: Introduce DMA-device device_caps callback Serge Semin
2020-05-29 12:12 ` Andy Shevchenko
2020-05-29 14:07 ` Serge Semin
2020-05-28 22:23 ` [PATCH v4 06/11] dmaengine: dw: Take HC_LLP flag into account for noLLP auto-config Serge Semin
2020-05-28 22:23 ` [PATCH v4 07/11] dmaengine: dw: Set DMA device max segment size parameter Serge Semin
2020-05-29 12:18 ` Andy Shevchenko
2020-05-28 22:23 ` [PATCH v4 08/11] dmaengine: dw: Add dummy device_caps callback Serge Semin
2020-05-29 12:19 ` Andy Shevchenko
2020-05-28 22:23 ` [PATCH v4 09/11] dmaengine: dw: Initialize min_burst capability Serge Semin
2020-05-29 10:25 ` Andy Shevchenko
2020-05-29 10:29 ` Andy Shevchenko
2020-05-29 10:41 ` Serge Semin
2020-05-29 10:50 ` Andy Shevchenko
2020-05-29 10:51 ` Serge Semin
2020-05-28 22:24 ` [PATCH v4 10/11] dmaengine: dw: Introduce max burst length hw config Serge Semin
2020-05-29 10:27 ` Andy Shevchenko
2020-05-28 22:24 ` Serge Semin [this message]
2020-05-29 10:27 ` [PATCH v4 11/11] dmaengine: dw: Initialize max_sg_nents capability Andy Shevchenko
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