Message-ID: <20200306133035.GB1748204@smile.fi.intel.com>
Date:   Fri, 6 Mar 2020 15:30:35 +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 03:29:12PM +0200, Andy Shevchenko wrote:
> 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.

One thing that I can tell immediately is the broken email thread in this series.
Whenever you do a series, use `git format-patch --cover-letter --thread ...`,
so, it will link the mail properly.

-- 
With Best Regards,
Andy Shevchenko

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