linux-kernel - Re: [PATCH 2/2] PCI: endpoint: pci-epf-vntb: simplify ctrl/spad space allocation

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Message-ID: <Z+qrWleCthbAfDxf@lizhi-Precision-Tower-5810>
Date: Mon, 31 Mar 2025 10:48:58 -0400
From: Frank Li <Frank.li@....com>
To: Jerome Brunet <jbrunet@...libre.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Jon Mason <jdmason@...zu.us>, Dave Jiang <dave.jiang@...el.com>,
	Allen Hubbe <allenbh@...il.com>,
	Marek Vasut <marek.vasut+renesas@...il.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Yuya Hamamachi <yuya.hamamachi.sx@...esas.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	ntb@...ts.linux.dev
Subject: Re: [PATCH 2/2] PCI: endpoint: pci-epf-vntb: simplify ctrl/spad
 space allocation

On Fri, Mar 28, 2025 at 03:53:43PM +0100, Jerome Brunet wrote:
> When allocating the shared ctrl/spad space, epf_ntb_config_spad_bar_alloc()
> should not try to handle the size quirks for the underlying BAR, whether it
> is fixed size or alignment. This is already handled by
> pci_epf_alloc_space().
>
> Also, when handling the alignment, this allocate more space than necessary.
> For example, with a spad size of 1024B and a ctrl size of 308B, the space
> necessary is 1332B. If the alignment is 1MB,
> epf_ntb_config_spad_bar_alloc() tries to allocate 2MB where 1MB would have
> been more than enough.
>
> Just drop all the handling of the BAR size quirks and let
> pci_epf_alloc_space() handle that.
>
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> ---
>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 24 ++----------------------
>  1 file changed, 2 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 874cb097b093ae645bbc4bf3c9d28ca812d7689d..c20a60fcb99e6e16716dd78ab59ebf7cf074b2a6 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -408,11 +408,9 @@ static void epf_ntb_config_spad_bar_free(struct epf_ntb *ntb)
>   */
>  static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
>  {
> -	size_t align;
>  	enum pci_barno barno;
>  	struct epf_ntb_ctrl *ctrl;
>  	u32 spad_size, ctrl_size;
> -	u64 size;
>  	struct pci_epf *epf = ntb->epf;
>  	struct device *dev = &epf->dev;
>  	u32 spad_count;
> @@ -422,31 +420,13 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
>  								epf->func_no,
>  								epf->vfunc_no);
>  	barno = ntb->epf_ntb_bar[BAR_CONFIG];
> -	size = epc_features->bar[barno].fixed_size;
> -	align = epc_features->align;
> -
> -	if ((!IS_ALIGNED(size, align)))
> -		return -EINVAL;
> -
>  	spad_count = ntb->spad_count;
>
>  	ctrl_size = sizeof(struct epf_ntb_ctrl);

I think keep ctrl_size at least align to 4 bytes. keep align 2^n is more
safe to keep spad area start at align possition.

	ctrl_size = roundup_pow_of_two(sizeof(struct epf_ntb_ctrl));

Frank

>  	spad_size = 2 * spad_count * sizeof(u32);
>
> -	if (!align) {
> -		ctrl_size = roundup_pow_of_two(ctrl_size);
> -		spad_size = roundup_pow_of_two(spad_size);
> -	} else {
> -		ctrl_size = ALIGN(ctrl_size, align);
> -		spad_size = ALIGN(spad_size, align);
> -	}
> -
> -	if (!size)
> -		size = ctrl_size + spad_size;
> -	else if (size < ctrl_size + spad_size)
> -		return -EINVAL;
> -
> -	base = pci_epf_alloc_space(epf, size, barno, epc_features, 0);
> +	base = pci_epf_alloc_space(epf, ctrl_size + spad_size,
> +				   barno, epc_features, 0);
>  	if (!base) {
>  		dev_err(dev, "Config/Status/SPAD alloc region fail\n");
>  		return -ENOMEM;
>
> --
> 2.47.2
>