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Date:   Thu, 12 Jan 2023 21:46:59 +0300
From:   Serge Semin <fancer.lancer@gmail.com>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Serge Semin <Sergey.Semin@baikalelectronics.ru>,
        Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
        Vinod Koul <vkoul@kernel.org>, Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Cai Huoqing <cai.huoqing@linux.dev>,
        Jingoo Han <jingoohan1@gmail.com>, Frank Li <Frank.Li@nxp.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
        Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
        caihuoqing <caihuoqing@baidu.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        linux-pci@vger.kernel.org, dmaengine@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 24/26] PCI: dwc: Set coherent DMA-mask on MSI-address
 allocation
Message-ID: <20230112184659.mwwjr4xg6ktskqhd@mobilestation>
References: <20221219144658.26620-1-Sergey.Semin@baikalelectronics.ru>
 <20221219144658.26620-25-Sergey.Semin@baikalelectronics.ru>
 <fa491b99-5e05-b436-9304-32baeb019750@arm.com>
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On Wed, Jan 11, 2023 at 01:39:35PM +0000, Robin Murphy wrote:
> On 2022-12-19 14:46, Serge Semin wrote:
> > The MSI target address requires to be reserved within the lowest 4GB
> > memory in order to support the PCIe peripherals with no 64-bit MSI TLPs
> > support. Since the allocation is done from the DMA-coherent memory let's
> > modify the allocation procedure to setting the coherent DMA-mask only and
> > avoiding the streaming DMA-mask modification. Thus at least the streaming
> > DMA operations would work with no artificial limitations. It will be
> > specifically useful for the eDMA-capable controllers so the corresponding
> > DMA-engine clients would map the DMA buffers with no need in the SWIOTLB
> > intervention for the buffers allocated above the 4GB memory region.
> > 
> > While at it let's add a brief comment about the reason of having the MSI
> > target address allocated from the DMA-coherent memory limited with the 4GB
> > upper bound.
> 
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>

Great! Thanks.

-Serge(y)

> 
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > 
> > ---
> > 
> > Changelog v8:
> > - This is a new patch added on v8 stage of the series.
> >    (@Robin, @Christoph)
> > ---
> >   drivers/pci/controller/dwc/pcie-designware-host.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 3ab6ae3712c4..e10608af39b4 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -366,7 +366,16 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
> >   						    dw_chained_msi_isr, pp);
> >   	}
> > -	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
> > +	/*
> > +	 * Even though the iMSI-RX Module supports 64-bit addresses some
> > +	 * peripheral PCIe devices may lack the 64-bit messages support. In
> > +	 * order not to miss MSI TLPs from those devices the MSI target address
> > +	 * has to be reserved within the lowest 4GB.
> > +	 * Note until there is a better alternative found the reservation is
> > +	 * done by allocating from the artificially limited DMA-coherent
> > +	 * memory.
> > +	 */
> > +	ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
> >   	if (ret)
> >   		dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");