linux-kernel - Re: [RFC PATCH v2 19/27] PCI: dwc: ep: Cache MSI outbound iATU mapping

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Message-ID: <aTATWZaiqwNfwymD@ryzen>
Date: Wed, 3 Dec 2025 11:39:21 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Koichiro Den <den@...inux.co.jp>
Cc: Frank Li <Frank.li@....com>, ntb@...ts.linux.dev,
	linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, mani@...nel.org,
	kwilczynski@...nel.org, kishon@...nel.org, bhelgaas@...gle.com,
	corbet@....net, vkoul@...nel.org, jdmason@...zu.us,
	dave.jiang@...el.com, allenbh@...il.com, Basavaraj.Natikar@....com,
	Shyam-sundar.S-k@....com, kurt.schwemmer@...rosemi.com,
	logang@...tatee.com, jingoohan1@...il.com, lpieralisi@...nel.org,
	robh@...nel.org, jbrunet@...libre.com, fancer.lancer@...il.com,
	arnd@...db.de, pstanner@...hat.com, elfring@...rs.sourceforge.net,
	Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [RFC PATCH v2 19/27] PCI: dwc: ep: Cache MSI outbound iATU
 mapping

On Wed, Dec 03, 2025 at 05:40:45PM +0900, Koichiro Den wrote:
> > 
> > If we want to improve the dw-edma driver, so that an EPF driver can have
> > multiple outstanding transfers, I think the best way forward would be to create
> > a new _prep_slave_memcpy() or similar, that does take a direction, and thus
> > does not require dmaengine_slave_config() to be called before every
> > _prep_slave_memcpy() call.
> 
> Would dmaengine_prep_slave_single_config(), which Frank tolds us in this
> thread, be sufficient?

I think that Frank is suggesting a new dmaengine API,
dmaengine_prep_slave_single_config(), which is like
dmaengine_prep_slave_single(), but also takes a struct dma_slave_config *
as a parameter.


I really like the idea.
I think it would allow us to remove the mutex in nvmet_pci_epf_dma_transfer():
https://github.com/torvalds/linux/blob/v6.18/drivers/nvme/target/pci-epf.c#L389-L429

Frank you wrote: "Thanks, we also consider ..."
Does that mean that you have any plans to work on this?
I would definitely be interested.


Kind regards,
Niklas