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Date:   Fri, 6 Mar 2020 16:47:20 +0300
From:   Sergey Semin <Sergey.Semin@baikalelectronics.ru>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
CC:     Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
        Maxim Kaurkin <Maxim.Kaurkin@baikalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
        Ekaterina Skachko <Ekaterina.Skachko@baikalelectronics.ru>,
        Vadim Vlasov <V.Vlasov@baikalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Paul Burton <paulburton@kernel.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        Viresh Kumar <vireshk@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Vinod Koul <vkoul@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        <dmaengine@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/5] dmaengine: dw: Take Baikal-T1 SoC DW DMAC
 peculiarities into account
References: <20200306131048.ADBE18030797@mail.baikalelectronics.ru>
 <20200306132912.GA1748204@smile.fi.intel.com>
 <20200306133756.0F74C8030793@mail.baikalelectronics.ru>
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On Fri, Mar 06, 2020 at 03:30:35PM +0200, Andy Shevchenko wrote:
> 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@baikalelectronics.ru wrote:
> > > From: Serge Semin <fancer.lancer@gmail.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.
> 

Hello Andy,
Thanks for the quick response. Looking forward to get the patches
reviewed and move on with the next patchset I'll send after this. It concerns
DW APB SSI driver, which uses the changes introduced by this one. So the
sooner we finished with this patchset the better. Although I understand
that it may take some time. I've just sent over 12 patchset, which have a lot
of fixups and new drivers.)

> 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.
> 

I've got thread=true in my gitconfig file, so each email should have
the proper reference and in-reply-to to the cover-letter (I see it from
the log). The problem popped up from a different place. For some reason the
automatic CC/To list extraction command didn't do the job right, so we ended
up with lacking of mailing lists in Cc's in this patchset. The command look like
this:

git send-email --cc-cmd "scripts/get_maintainer.pl --separator , --nokeywords --nogit --nogit-fallback --norolestats --nom" \
                   --to-cmd "scripts/get_maintainer.pl --separator , --nokeywords --nogit --nogit-fallback --norolestats --nol" \
                   --from "Serge Semin <Sergey.Semin at baikalelectronics.ru>" \
                   --smtp-server-option="-abaikal" --cover-letter -5

Regards,
-Sergey

> -- 
> With Best Regards,
> Andy Shevchenko
> 
>