Re: [PATCH v2 3/7] PCI: Honor alignment overrides
From: Jani Nikula
Date: Fri Oct 02 2026 - 07:47:16 EST
On Fri, 02 Oct 2026, Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> wrote:
> pci=resource_alignment argument can override the default alignment for
> the resource. The remainder code introduced in the commit 9036bd0efcb6
> ("PCI: Align head space better") can move remainder space (non-aligning
> part of the size) before the aligning left edge which results in
> violating the requested alignment.
>
> Introduce struct pci_resreq_data to hold device and user-given alignment
> to be able to honor it in pci_align_resource(). When user-given alignment
> is found, any remainder movement is skipped.
>
> Fixes: 9036bd0efcb6 ("PCI: Align head space better")
> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> Link: https://lore.kernel.org/linux-pci/20260923133202.07DF61F000FF@xxxxxxxxxxxxxxx/
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
So I don't have the time to figure out what's going on here, but
assuming you get proper review, the i915 part is
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
for merging via whichever tree makes sense.
> ---
> arch/alpha/kernel/pci.c | 3 ++-
> arch/arm/kernel/bios32.c | 5 +++--
> arch/m68k/kernel/pcibios.c | 4 ++--
> arch/mips/pci/pci-generic.c | 5 +++--
> arch/mips/pci/pci-legacy.c | 5 +++--
> arch/parisc/kernel/pci.c | 5 +++--
> arch/powerpc/kernel/pci-common.c | 5 +++--
> arch/sh/drivers/pci/pci.c | 5 +++--
> arch/x86/pci/i386.c | 5 +++--
> arch/xtensa/kernel/pci.c | 5 +++--
> drivers/char/agp/intel-gtt.c | 5 ++++-
> drivers/gpu/drm/i915/i915_gmch.c | 5 +++--
> drivers/pci/pci.c | 5 +++--
> drivers/pci/setup-res.c | 19 +++++++++++++------
> include/linux/pci.h | 26 ++++++++++++++++++++++++--
> 15 files changed, 75 insertions(+), 32 deletions(-)
>
> diff --git a/arch/alpha/kernel/pci.c b/arch/alpha/kernel/pci.c
> index 11df411b1d18..c5d725a9781f 100644
> --- a/arch/alpha/kernel/pci.c
> +++ b/arch/alpha/kernel/pci.c
> @@ -128,7 +128,8 @@ pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size, resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> struct pci_controller *hose = dev->sysdata;
> unsigned long alignto;
> resource_size_t start = res->start;
> diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
> index ac0e890510da..3e61826f07fb 100644
> --- a/arch/arm/kernel/bios32.c
> +++ b/arch/arm/kernel/bios32.c
> @@ -564,7 +564,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> resource_size_t size,
> resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t start = res->start;
> struct pci_host_bridge *host_bridge;
>
> @@ -578,7 +579,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> start, size, align);
>
> if (res->flags & IORESOURCE_MEM)
> - return pci_align_resource(dev, res, empty_res, size, align);
> + return pci_align_resource(rr, res, empty_res, size, align);
>
> return start;
> }
> diff --git a/arch/m68k/kernel/pcibios.c b/arch/m68k/kernel/pcibios.c
> index 7a9e60df79c5..3024408412bc 100644
> --- a/arch/m68k/kernel/pcibios.c
> +++ b/arch/m68k/kernel/pcibios.c
> @@ -31,14 +31,14 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> resource_size_t size,
> resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> resource_size_t start = res->start;
>
> if ((res->flags & IORESOURCE_IO) && (start & 0x300))
> start = (start + 0x3ff) & ~0x3ff;
>
> if (res->flags & IORESOURCE_MEM)
> - return pci_align_resource(dev, res, empty_res, size, align);
> + return pci_align_resource(rr, res, empty_res, size, align);
>
> return start;
> }
> diff --git a/arch/mips/pci/pci-generic.c b/arch/mips/pci/pci-generic.c
> index c2e23d0c1d77..7f3ecb91b85b 100644
> --- a/arch/mips/pci/pci-generic.c
> +++ b/arch/mips/pci/pci-generic.c
> @@ -25,7 +25,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size, resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t start = res->start;
> struct pci_host_bridge *host_bridge;
>
> @@ -39,7 +40,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> start, size, align);
>
> if (res->flags & IORESOURCE_MEM)
> - return pci_align_resource(dev, res, empty_res, size, align);
> + return pci_align_resource(rr, res, empty_res, size, align);
>
> return start;
> }
> diff --git a/arch/mips/pci/pci-legacy.c b/arch/mips/pci/pci-legacy.c
> index dae6dafdd6e0..82d4b01db64e 100644
> --- a/arch/mips/pci/pci-legacy.c
> +++ b/arch/mips/pci/pci-legacy.c
> @@ -55,7 +55,8 @@ pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size, resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> struct pci_controller *hose = dev->sysdata;
> resource_size_t start = res->start;
>
> @@ -70,7 +71,7 @@ pcibios_align_resource(void *data, const struct resource *res,
> if (start & 0x300)
> start = (start + 0x3ff) & ~0x3ff;
> } else if (res->flags & IORESOURCE_MEM) {
> - start = pci_align_resource(dev, res, empty_res, size, align);
> + start = pci_align_resource(rr, res, empty_res, size, align);
>
> /* Make sure we start at our min on all hoses */
> if (start < PCIBIOS_MIN_MEM + hose->mem_resource->start)
> diff --git a/arch/parisc/kernel/pci.c b/arch/parisc/kernel/pci.c
> index 518f532ccddc..d582be996051 100644
> --- a/arch/parisc/kernel/pci.c
> +++ b/arch/parisc/kernel/pci.c
> @@ -193,7 +193,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> resource_size_t size,
> resource_size_t alignment)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t align, start = res->start;
>
> pci_dbg(dev, "%pR: pcibios_align_resource(%lx, 0x%llx, 0x%llx), parent %pR\n",
> @@ -205,7 +206,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> if (align > alignment)
> start = ALIGN(start, align);
> else
> - start = pci_align_resource(dev, res, empty_res, size, alignment);
> + start = pci_align_resource(rr, res, empty_res, size, alignment);
>
> return start;
> }
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 4fc52c21fe5d..23594759cfe2 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -1131,7 +1131,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> resource_size_t size,
> resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t start = res->start;
>
> if (res->flags & IORESOURCE_IO) {
> @@ -1140,7 +1141,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> if (start & 0x300)
> start = (start + 0x3ff) & ~0x3ff;
> } else if (res->flags & IORESOURCE_MEM) {
> - start = pci_align_resource(dev, res, empty_res, size, align);
> + start = pci_align_resource(rr, res, empty_res, size, align);
> }
>
> return start;
> diff --git a/arch/sh/drivers/pci/pci.c b/arch/sh/drivers/pci/pci.c
> index 878a27a1acfb..279f2770ff4b 100644
> --- a/arch/sh/drivers/pci/pci.c
> +++ b/arch/sh/drivers/pci/pci.c
> @@ -172,7 +172,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> resource_size_t size,
> resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> struct pci_channel *hose = dev->sysdata;
> resource_size_t start = res->start;
>
> @@ -186,7 +187,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> if (start & 0x300)
> start = (start + 0x3ff) & ~0x3ff;
> } else if (res->flags & IORESOURCE_MEM) {
> - start = pci_align_resource(dev, res, empty_res, size, align);
> + start = pci_align_resource(rr, res, empty_res, size, align);
> }
>
> return start;
> diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
> index e2de26b82940..4178ae4380c2 100644
> --- a/arch/x86/pci/i386.c
> +++ b/arch/x86/pci/i386.c
> @@ -156,7 +156,8 @@ pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size, resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t start = res->start;
>
> if (res->flags & IORESOURCE_IO) {
> @@ -165,7 +166,7 @@ pcibios_align_resource(void *data, const struct resource *res,
> if (start & 0x300)
> start = (start + 0x3ff) & ~0x3ff;
> } else if (res->flags & IORESOURCE_MEM) {
> - start = pci_align_resource(dev, res, empty_res, size, align);
> + start = pci_align_resource(rr, res, empty_res, size, align);
>
> /* The low 1MB range is reserved for ISA cards */
> if (start < BIOS_END)
> diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
> index 305031551136..4e8ad4a3c9fe 100644
> --- a/arch/xtensa/kernel/pci.c
> +++ b/arch/xtensa/kernel/pci.c
> @@ -42,7 +42,8 @@ pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size, resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
> + struct pci_dev *dev = rr->dev;
> resource_size_t start = res->start;
>
> if (res->flags & IORESOURCE_IO) {
> @@ -55,7 +56,7 @@ pcibios_align_resource(void *data, const struct resource *res,
> if (start & 0x300)
> start = (start + 0x3ff) & ~0x3ff;
> } else if (res->flags & IORESOURCE_MEM) {
> - start = pci_align_resource(dev, res, empty_res, size, align);
> + start = pci_align_resource(rr, res, empty_res, size, align);
> }
>
> return start;
> diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
> index bcc26785175d..2214347906a6 100644
> --- a/drivers/char/agp/intel-gtt.c
> +++ b/drivers/char/agp/intel-gtt.c
> @@ -1038,10 +1038,13 @@ static struct agp_memory *intel_fake_agp_alloc_by_type(size_t pg_count,
>
> static int intel_alloc_chipset_flush_resource(void)
> {
> + struct pci_resreq_data rr;
> int ret;
> +
> + pci_init_pci_resreq_data(&rr, intel_private.bridge_dev);
> ret = pci_bus_alloc_resource(intel_private.bridge_dev->bus, &intel_private.ifp_resource, PAGE_SIZE,
> PAGE_SIZE, PCIBIOS_MIN_MEM, 0,
> - pcibios_align_resource, intel_private.bridge_dev);
> + pcibios_align_resource, &rr);
>
> return ret;
> }
> diff --git a/drivers/gpu/drm/i915/i915_gmch.c b/drivers/gpu/drm/i915/i915_gmch.c
> index b0ef6ef577a3..d35097bebc0f 100644
> --- a/drivers/gpu/drm/i915/i915_gmch.c
> +++ b/drivers/gpu/drm/i915/i915_gmch.c
> @@ -38,6 +38,7 @@ static int mchbar_reg(struct drm_i915_private *i915)
> static int
> intel_alloc_mchbar_resource(struct drm_i915_private *i915)
> {
> + struct pci_resreq_data rr;
> u32 temp_lo, temp_hi = 0;
> u64 mchbar_addr;
> int ret;
> @@ -55,12 +56,12 @@ intel_alloc_mchbar_resource(struct drm_i915_private *i915)
> /* Get some space for it */
> i915->gmch.mch_res.name = "i915 MCHBAR";
> i915->gmch.mch_res.flags = IORESOURCE_MEM;
> + pci_init_pci_resreq_data(&rr, i915->gmch.pdev);
> ret = pci_bus_alloc_resource(i915->gmch.pdev->bus,
> &i915->gmch.mch_res,
> MCHBAR_SIZE, MCHBAR_SIZE,
> PCIBIOS_MIN_MEM,
> - 0, pcibios_align_resource,
> - i915->gmch.pdev);
> + 0, pcibios_align_resource, &rr);
> if (ret) {
> drm_dbg(&i915->drm, "failed bus alloc: %d\n", ret);
> i915->gmch.mch_res.start = 0;
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b2879a6be5f8..1b7a4469c6ca 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6444,8 +6444,8 @@ static DEFINE_SPINLOCK(resource_alignment_lock);
> * RETURNS: Resource alignment if it is specified.
> * Zero if it is not specified.
> */
> -static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> - bool *resize)
> +resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> + bool *resize)
> {
> int align_order, count;
> resource_size_t align = pcibios_default_alignment();
> @@ -6497,6 +6497,7 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> spin_unlock(&resource_alignment_lock);
> return align;
> }
> +EXPORT_SYMBOL_GPL(pci_specified_resource_alignment);
>
> static void pci_request_resource_alignment(struct pci_dev *dev, int bar,
> resource_size_t align, bool resize)
> diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> index 376f09630a4a..441a62807719 100644
> --- a/drivers/pci/setup-res.c
> +++ b/drivers/pci/setup-res.c
> @@ -265,17 +265,21 @@ resource_size_t pci_resource_alignment(const struct pci_dev *dev,
> * before res->start if there's enough free space there. This enables
> * tighter packing for resources.
> */
> -resource_size_t pci_align_resource(struct pci_dev *dev,
> +resource_size_t pci_align_resource(struct pci_resreq_data *rr,
> const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size,
> resource_size_t align)
> {
> + struct pci_dev *dev = rr->dev;
> resource_size_t remainder, start_addr;
>
> if (!(res->flags & IORESOURCE_MEM))
> return res->start;
>
> + if (rr->user_align)
> + return res->start;
> +
> if (IS_ALIGNED(size, align))
> return res->start;
>
> @@ -306,18 +310,21 @@ resource_size_t __weak pcibios_align_resource(void *data,
> resource_size_t size,
> resource_size_t align)
> {
> - struct pci_dev *dev = data;
> + struct pci_resreq_data *rr = data;
>
> - return pci_align_resource(dev, res, empty_res, size, align);
> + return pci_align_resource(rr, res, empty_res, size, align);
> }
>
> static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
> int resno, resource_size_t size, resource_size_t align)
> {
> struct resource *res = pci_resource_n(dev, resno);
> + struct pci_resreq_data rr;
> resource_size_t min;
> int ret;
>
> + pci_init_pci_resreq_data(&rr, dev);
> +
> min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
>
> /*
> @@ -329,7 +336,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
> */
> ret = pci_bus_alloc_resource(bus, res, size, align, min,
> IORESOURCE_PREFETCH | IORESOURCE_MEM_64,
> - pcibios_align_resource, dev);
> + pcibios_align_resource, &rr);
> if (ret == 0)
> return 0;
>
> @@ -341,7 +348,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
> (IORESOURCE_PREFETCH | IORESOURCE_MEM_64)) {
> ret = pci_bus_alloc_resource(bus, res, size, align, min,
> IORESOURCE_PREFETCH,
> - pcibios_align_resource, dev);
> + pcibios_align_resource, &rr);
> if (ret == 0)
> return 0;
> }
> @@ -354,7 +361,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
> */
> if (res->flags & (IORESOURCE_PREFETCH | IORESOURCE_MEM_64))
> ret = pci_bus_alloc_resource(bus, res, size, align, min, 0,
> - pcibios_align_resource, dev);
> + pcibios_align_resource, &rr);
>
> return ret;
> }
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index d31a8d107b1e..fe0233f0d9e6 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1217,12 +1217,34 @@ int __must_check pcibios_enable_device(struct pci_dev *, int mask);
> /* Architecture-specific versions may override this (weak) */
> char *pcibios_setup(char *str);
>
> -/* Used only when drivers/pci/setup.c is used */
> +/* Resource assignment request handling */
> +/**
> + * struct pci_resreq_data - Data passed to pcibios_align_resource()
> + * @dev: PCI device
> + * @user_align: User provided alignment override (pci=resource_alignment param)
> + */
> +struct pci_resreq_data {
> + struct pci_dev *dev;
> + resource_size_t user_align;
> +};
> +
> +resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> + bool *resize);
> +static inline void pci_init_pci_resreq_data(struct pci_resreq_data *rr,
> + struct pci_dev *dev)
> +{
> + bool user_aligned;
> +
> + memset(rr, 0, sizeof(*rr));
> + rr->dev = dev;
> + rr->user_align = pci_specified_resource_alignment(dev, &user_aligned);
> +}
> +
> resource_size_t pcibios_align_resource(void *data, const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size,
> resource_size_t align);
> -resource_size_t pci_align_resource(struct pci_dev *dev,
> +resource_size_t pci_align_resource(struct pci_resreq_data *rr,
> const struct resource *res,
> const struct resource *empty_res,
> resource_size_t size,
--
Jani Nikula, Intel