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Date: Thu, 17 Mar 2022 11:17:57 +0100 From: Yann Gautier <yann.gautier@...s.st.com> To: Ulf Hansson <ulf.hansson@...aro.org> CC: Linus Walleij <linus.walleij@...aro.org>, Rob Herring <robh+dt@...nel.org>, <devicetree@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, Christophe Kerello <christophe.kerello@...s.st.com>, Ludovic Barre <ludovic.barre@...s.st.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, Philipp Zabel <p.zabel@...gutronix.de>, Russell King <linux@...linux.org.uk>, Marek Vasut <marex@...x.de>, <kernel@...electronics.com>, Manivannan Sadhasivam <mani@...nel.org>, Grzegorz Szymaszek <gszymaszek@...rt.pl> Subject: Re: [PATCH 1/3] dt-bindings: mmc: mmci: add a property to disable DMA LLI On 3/17/22 11:00, Ulf Hansson wrote: > On Tue, 15 Mar 2022 at 09:26, Yann Gautier <yann.gautier@...s.st.com> wrote: >> >> On 3/14/22 23:43, Linus Walleij wrote: >>> "On Fri, Mar 4, 2022 at 2:52 PM Yann Gautier <yann.gautier@...s.st.com> wrote: >>> >>>> On STMicroelectronics variant of PL18x, the DMA Linked Lists are supported >>>> starting from revision v2 of the peripheral. But it has limitations, >>>> as all the buffers should be aligned on block size (except the last one). >>>> But this cannot be guaranteed with SDIO. We should then have a property >>>> to disable the support of LLI. >>>> >>>> Signed-off-by: Yann Gautier <yann.gautier@...s.st.com> >>> >>> Actually I think this is present also on the ux500 variants. See: >>> commit 2253ed4b36dc876d1598c4dab5587e537ec68c34 >>> "mmc: mmci: Support any block sizes for ux500v2 and qcom variant" >>> >>> Spot the variant data "dma_power_of_2". >>> >>> So whatever property you add >>> to the variant data (not in the device tree please) should >>> be added to the ux500 variants as well, it will *VERY* likely >>> have a problem with LLI elements not being a power of 2 >>> as it is the ancestor of later STMicro variants. >>> >>> It might actually be the reason for some annoying WiFi error >>> messages I have seen :/ >>> >>> Yours, >>> Linus Walleij >> >> Hi Linus, >> >> The STM32 variant uses an internal DMA, and the DMA functions are in its >> dedicated file. So I was planning to do the same as what is done in >> meson-gx-mmc.c: using a bounce buffer to copy from/to in case DMA >> constraints are not fulfilled. Not sure it can help for Ux500. > Hi Ulf, > We already have a bounce buffer in mmci_pio_read(), but we need one in > mmc_pio_write() too, which hasn't been implemented yet. The idea is to keep using our internal DMA, and not switch to pio mode. > >> >> Ulf, before I send my new series (although it is not ready yet), would >> you be OK with the bounce buffer idea? > > Yes, that works for me. I have patches almost ready, I'll send that soon. > > On the other hand, it would be even better if we could specify the > buffer limitations per mmc host instance, so upper layers (SDIO func > drivers) could conform to these - and use better buffers, to achieve a > better performance. We've seen things that could be improved in the wifi driver. I'll check what could be done. Best regards, Yann > >> >> >> Best regards, >> Yann > > Kind regards > Uffe
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