From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Mark Brown <broonie@kernel.org>,
Linus Walleij <linus.walleij@stericsson.com>,
Vinod Koul <vkoul@kernel.org>, Feng Tang <feng.tang@intel.com>,
Grant Likely <grant.likely@secretlab.ca>,
Alan Cox <alan@linux.intel.com>,
Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>,
Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Paul Burton <paulburton@kernel.org>,
Ralf Baechle <ralf@linux-mips.org>, Arnd Bergmann <arnd@arndb.de>,
Rob Herring <robh+dt@kernel.org>,
linux-mips@vger.kernel.org, devicetree@vger.kernel.org,
Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jarkko Nikula <jarkko.nikula@linux.intel.com>,
"wuxu.wu" <wuxu.wu@huawei.com>, Clement Leger <cleger@kalray.eu>,
Linus Walleij <linus.walleij@linaro.org>,
linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 01/16] spi: dw: Add Tx/Rx finish wait methods to the MID DMA
Date: Fri, 22 May 2020 17:36:39 +0300 [thread overview]
Message-ID: <20200522143639.GG1634618@smile.fi.intel.com> (raw)
In-Reply-To: <20200522140025.bmd6bhpjjk5msvsm@mobilestation>
On Fri, May 22, 2020 at 05:00:25PM +0300, Serge Semin wrote:
> On Fri, May 22, 2020 at 04:27:43PM +0300, Serge Semin wrote:
> > On Fri, May 22, 2020 at 02:10:13PM +0100, Mark Brown wrote:
> > > On Fri, May 22, 2020 at 03:44:06PM +0300, Serge Semin wrote:
> > > > On Fri, May 22, 2020 at 03:34:27PM +0300, Andy Shevchenko wrote:
...
> > > > > > Realistically it seems unlikely that the clock will be even as slow as
> > > > > > double digit kHz though, and if we do I'd not be surprised to see other
> > > > > > problems kicking in. It's definitely good to handle such things if we
> > > > > > can but so long as everything is OK for realistic use cases I'm not sure
> > > > > > it should be a blocker.
> > >
> > > > As I see it the only way to fix the problem for any use-case is to move the
> > > > busy-wait loop out from the tasklet's callback, add a completion variable to the
> > > > DW SPI data and wait for all the DMA transfers completion in the
> > > > dw_spi_dma_transfer() method. Then execute both busy-wait loops (there we can
> > > > use spi_delay_exec() since it's a work-thread) and call
> > > > spi_finalize_current_transfer() after it. What do you think?
> > >
> > > I'm concerned that this will add latency for the common case to handle a
> > > potential issue for unrealistically slow buses but yeah, if it's an
> > > issue kicking up to task context is how you'd handle it.
> >
> > I am not that worried about the latency (most likely it'll be the same as
> > before), but I am mostly concerned regarding a most likely need to re-implement
> > a local version spi_transfer_wait(). We can't afford wait for the completion
> > indefinitely here, so the wait_for_completion_timeout() should be used, for which
> > I would have to calculate a decent timeout based on the transfer capabilities,
> > etc. So basically it would mean to partly copy the spi_transfer_wait() to this
> > module.(
>
> I'd also wait for Andy's suggestion regarding this, since he's been worried
> about the delay length in the first place. So he may come up with a better
> solution in this regard.
The completion approach sounds quite heavy to me.
Since we haven't got any report for such an issue, I prefer as simplest as
possible approach.
If we add might_sleep() wouldn't it be basically reimplementation of the
spi_delay_exec() again?
And second question, do you experience this warning on your system?
My point is: let's warn and see if anybody comes with a bug report. We will
solve an issue when it appears.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-05-22 14:36 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 0:07 [PATCH v4 00/16] spi: dw: Add generic DW DMA controller support Serge Semin
2020-05-22 0:07 ` [PATCH v4 02/16] spi: dw: Enable interrupts in accordance with DMA xfer mode Serge Semin
2020-05-22 0:07 ` [PATCH v4 04/16] spi: dw: Discard unused void priv pointer Serge Semin
2020-05-22 0:07 ` [PATCH v4 06/16] spi: dw: Parameterize the DMA Rx/Tx burst length Serge Semin
2020-05-22 11:06 ` Andy Shevchenko
2020-05-22 0:07 ` [PATCH v4 07/16] spi: dw: Use DMA max burst to set the request thresholds Serge Semin
2020-05-22 0:08 ` [PATCH v4 11/16] spi: dw: Remove DW DMA code dependency from DW_DMAC_PCI Serge Semin
2020-05-22 0:08 ` [PATCH v4 12/16] spi: dw: Add DW SPI DMA/PCI/MMIO dependency on the DW SPI core Serge Semin
2020-05-22 11:07 ` Andy Shevchenko
2020-05-22 11:08 ` Andy Shevchenko
2020-05-22 0:08 ` [PATCH v4 14/16] spi: dw: Add DMA support to the DW SPI MMIO driver Serge Semin
2020-05-22 0:08 ` [PATCH v4 16/16] dt-bindings: spi: Convert DW SPI binding to DT schema Serge Semin
2020-05-28 23:28 ` Rob Herring
[not found] ` <20200522000806.7381-2-Sergey.Semin@baikalelectronics.ru>
2020-05-22 11:13 ` [PATCH v4 01/16] spi: dw: Add Tx/Rx finish wait methods to the MID DMA Andy Shevchenko
[not found] ` <20200522115235.rt3ay7lveimrgooa@mobilestation>
2020-05-22 12:10 ` Mark Brown
2020-05-22 12:12 ` Andy Shevchenko
2020-05-22 12:18 ` Mark Brown
2020-05-22 12:34 ` Andy Shevchenko
[not found] ` <20200522124406.co7gmteojfsooerc@mobilestation>
[not found] ` <20200522131013.GH5801@sirena.org.uk>
[not found] ` <20200522132742.taf2ixfjpyd5u3dt@mobilestation>
[not found] ` <20200522140025.bmd6bhpjjk5msvsm@mobilestation>
2020-05-22 14:36 ` Andy Shevchenko [this message]
[not found] ` <20200522144542.brhibh453wid2d6v@mobilestation>
2020-05-22 15:22 ` Mark Brown
2020-05-23 8:34 ` Serge Semin
2020-05-25 11:41 ` Mark Brown
2020-05-25 21:36 ` Serge Semin
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