linux-kernel - Re: [PATCH 0/5] dmaengine: dw: Take Baikal-T1 SoC DW DMAC peculiarities into account

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Date:   Fri, 6 Mar 2020 15:29:12 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Sergey.Semin@...kalelectronics.ru
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Maxim Kaurkin <Maxim.Kaurkin@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Ekaterina Skachko <Ekaterina.Skachko@...kalelectronics.ru>,
        Vadim Vlasov <V.Vlasov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] dmaengine: dw: Take Baikal-T1 SoC DW DMAC
 peculiarities into account

On Fri, Mar 06, 2020 at 04:10:29PM +0300, Sergey.Semin@...kalelectronics.ru wrote:
> From: Serge Semin <fancer.lancer@...il.com>
> 
> Baikal-T1 SoC has an DW DMAC on-board to provide a Mem-to-Mem, low-speed
> peripherals Dev-to-Mem and Mem-to-Dev functionality. Mostly it's compatible
> with currently implemented in the kernel DW DMAC driver, but there are some
> peculiarities which must be taken into account in order to have the device
> fully supported.
> 
> First of all traditionally we replaced the legacy plain text-based dt-binding
> file with yaml-based one. Secondly Baikal-T1 DW DMA Controller provides eight
> channels, which alas have different max burst length configuration.
> In particular first two channels may burst up to 128 bits (16 bytes) at a time
> while the rest of them just up to 32 bits. We must make sure that the DMA
> subsystem doesn't set values exceeding these limitations otherwise the
> controller will hang up. In third currently we discovered the problem in using
> the DW APB SPI driver together with DW DMAC. The problem happens if there is no
> natively implemented multi-block LLP transfers support and the SPI-transfer
> length exceeds the max lock size. In this case due to asynchronous handling of
> Tx- and Rx- SPI transfers interrupt we might end up with Dw APB SSI Rx FIFO
> overflow. So if DW APB SSI (or any other DMAC service consumer) intends to use
> the DMAC to asynchronously execute the transfers we'd have to at least warn
> the user of the possible errors.
> 
> Finally there is a bug in the algorithm of the nollp flag detection.
> In particular even if DW DMAC parameters state the multi-block transfers
> support there is still HC_LLP (hardcode LLP) flag, which if set makes expected
> by the driver true multi-block LLP functionality unusable. This happens cause'
> if HC_LLP flag is set the LLP registers will be hardcoded to zero so the
> contiguous multi-block transfers will be only supported. We must take the
> flag into account when detecting the LLP support otherwise the driver just
> won't work correctly.
> 
> This patchset is rebased and tested on the mainline Linux kernel 5.6-rc4:
> commit 98d54f81e36b ("Linux 5.6-rc4").

Thank you for your series!

I'll definitely review it, but it will take time. So, I think due to late
submission this is material at least for v5.8.

> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Signed-off-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Maxim Kaurkin <Maxim.Kaurkin@...kalelectronics.ru>
> Cc: Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>
> Cc: Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>
> Cc: Ekaterina Skachko <Ekaterina.Skachko@...kalelectronics.ru>
> Cc: Vadim Vlasov <V.Vlasov@...kalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Paul Burton <paulburton@...nel.org>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Viresh Kumar <vireshk@...nel.org>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Vinod Koul <vkoul@...nel.org>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: dmaengine@...r.kernel.org
> Cc: devicetree@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> 
> Serge Semin (5):
>   dt-bindings: dma: dw: Replace DW DMAC legacy bindings with YAML-based
>     one
>   dt-bindings: dma: dw: Add max burst transaction length property
>     bindings
>   dmaengine: dw: Add LLP and block size config accessors
>   dmaengine: dw: Introduce max burst length hw config
>   dmaengine: dw: Take HC_LLP flag into account for noLLP auto-config
> 
>  .../bindings/dma/snps,dma-spear1340.yaml      | 180 ++++++++++++++++++
>  .../devicetree/bindings/dma/snps-dma.txt      |  69 -------
>  drivers/dma/dw/core.c                         |  24 ++-
>  drivers/dma/dw/dw.c                           |   1 +
>  drivers/dma/dw/of.c                           |   9 +
>  drivers/dma/dw/regs.h                         |   3 +
>  include/linux/platform_data/dma-dw.h          |  22 +++
>  7 files changed, 238 insertions(+), 70 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/dma/snps,dma-spear1340.yaml
>  delete mode 100644 Documentation/devicetree/bindings/dma/snps-dma.txt
> 
> -- 
> 2.25.1
> 

-- 
With Best Regards,
Andy Shevchenko