Subject: Re: [PATCH v2] cxl: Export AFU error buffer via sysfs

From: Michael Neuling <[email-masked]>
Date: Wed, 20 May 2015 22:12:44 +1000

On Wed, 2015-05-20 at 16:26 +0530, Vaibhav Jain wrote:
> Export the "AFU Error Buffer" via sysfs attribute (afu_err_buf). AFU
> error buffer is used by the AFU to report application specific
> errors. The contents of this buffer are AFU specific and are intended to
> be interpreted by the application interacting with the afu.
> 
> Testing:
> 	- Build against pseries le/be configs.
> 	- Run testing with a special version of memcpy afu on a 'be'
> 	kernel.
> 
> Change-log:
> v1 -> v2
> 	- Simplified cxl_afu_read_err_buffer to handle unaligned reads
> 	by performing a short read.
> 
> Signed-off-by: Vaibhav Jain <[email-masked]>
> ---
>  Documentation/ABI/testing/sysfs-class-cxl | 11 ++++++
>  drivers/misc/cxl/cxl.h                    |  7 ++++
>  drivers/misc/cxl/pci.c                    | 60 +++++++++++++++++++++++++++++++
>  drivers/misc/cxl/sysfs.c                  | 33 +++++++++++++++++
>  4 files changed, 111 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-cxl b/Documentation/ABI/testing/sysfs-class-cxl
> index d46bba8..45e9ce3 100644
> --- a/Documentation/ABI/testing/sysfs-class-cxl
> +++ b/Documentation/ABI/testing/sysfs-class-cxl
> @@ -6,6 +6,17 @@ Example: The real path of the attribute /sys/class/cxl/afu0.0s/irqs_max is
>  
>  Slave contexts (eg. /sys/class/cxl/afu0.0s):
>  
> +What:           /sys/class/cxl/<afu>/afu_err_buf
> +Date:           September 2014
> +Contact:        [email-masked]
> +Description:    read only
> +                AFU Error Buffer contents. The contents of this file are
> +		application specific and depends on the AFU being used.
> +		Applications interacting with the AFU can use this attribute
> +		to know about the current error condition and take appropriate
> +		action like logging the event etc.
> +
> +
>  What:           /sys/class/cxl/<afu>/irqs_max
>  Date:           September 2014
>  Contact:        [email-masked]
> diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h
> index a1cee47..789f077 100644
> --- a/drivers/misc/cxl/cxl.h
> +++ b/drivers/misc/cxl/cxl.h
> @@ -362,6 +362,10 @@ struct cxl_afu {
>  	struct mutex spa_mutex;
>  	spinlock_t afu_cntl_lock;
>  
> +	/* AFU error buffer fields and bin attribute for sysfs */
> +	u64 eb_len, eb_offset;
> +	struct bin_attribute attr_eb;
> +
>  	/*
>  	 * Only the first part of the SPA is used for the process element
>  	 * linked list. The only other part that software needs to worry about
> @@ -563,6 +567,9 @@ static inline void __iomem *_cxl_p2n_addr(struct cxl_afu *afu, cxl_p2n_reg_t reg
>  u16 cxl_afu_cr_read16(struct cxl_afu *afu, int cr, u64 off);
>  u8 cxl_afu_cr_read8(struct cxl_afu *afu, int cr, u64 off);
>  
> +ssize_t cxl_afu_read_err_buffer(struct cxl_afu *afu, char *buf,
> +				loff_t off, size_t count);
> +
>  
>  struct cxl_calls {
>  	void (*cxl_slbia)(struct mm_struct *mm);
> diff --git a/drivers/misc/cxl/pci.c b/drivers/misc/cxl/pci.c
> index 1ef0164..162a8fc 100644
> --- a/drivers/misc/cxl/pci.c
> +++ b/drivers/misc/cxl/pci.c
> @@ -593,6 +593,22 @@ static int cxl_read_afu_descriptor(struct cxl_afu *afu)
>  	afu->crs_len = AFUD_CR_LEN(val) * 256;
>  	afu->crs_offset = AFUD_READ_CR_OFF(afu);
>  
> +
> +	/* eb_len is in multiple of 4K */
> +	afu->eb_len = AFUD_EB_LEN(AFUD_READ_EB(afu)) * 4096;
> +	afu->eb_offset = AFUD_READ_EB_OFF(afu);
> +
> +	/* eb_off is 4K aligned so lower 12 bits are always zero */
> +	if (EXTRACT_PPC_BITS(afu->eb_offset, 0, 11) != 0) {
> +		dev_warn(&afu->dev,
> +			 "Invalid AFU error buffer offset %Lx\n",
> +			 afu->eb_offset);
> +		dev_info(&afu->dev,
> +			 "Ignoring AFU error buffer in the descriptor\n");
> +		/* indicate that no afu buffer exists */
> +		afu->eb_len = 0;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -672,6 +688,50 @@ static int sanitise_afu_regs(struct cxl_afu *afu)
>  	return 0;
>  }
>  
> +/*
> + * afu_eb_read:
> + * Called from sysfs and reads the afu error info buffer. The h/w only supports
> + * 4/8 bytes aligned access. So most of the code tries to get around this by
> + * reading full 8 bytes aligned chunks, copying it to a temp buffer and dropping
> + * unneeded bytes at the beginning & the end of the requested region.
> + */
> +ssize_t cxl_afu_read_err_buffer(struct cxl_afu *afu, char *buf,
> +				loff_t off, size_t count)
> +{
> +	u8 tbuff[8];
> +	const void __iomem *ebuf = afu->afu_desc_mmio + afu->eb_offset;
> +
> +	count = min((size_t)(afu->eb_len - off), count);
> +
> +	if (unlikely(count <= 0)) {
> +		/* handle case where no ebuf exists or offset out of bound */
> +		count = 0;
> +
> +	} else if ((count >= 8) && IS_ALIGNED(off, 8)) {
> +		/* read all the intermediate aligned words */
> +
> +		count = round_down(off + count, 8) - off;
> +		_memcpy_fromio(buf,
> +			       ebuf + off, count);
> +
> +	} else if (!IS_ALIGNED(off, 8)) {
> +		/* handle unaligned access at the beginning */
> +		_memcpy_fromio(tbuff, ebuf + round_down(off, 8), 8);
> +
> +		count = min((size_t)(ALIGN(off, 8) - off), count);
> +		memcpy(buf, tbuff + (off & 0x7), count);
> +
> +	} else {
> +		/* offset is aligned but count < 8 */
> +		_memcpy_fromio(tbuff, ebuf + round_down(off + count, 8), 8);
> +
> +		count = (off + count) - round_down(off + count, 8);
> +		memcpy(buf, tbuff, count);
> +	}

I still think this is too complex.  How about something like this where
we always use a copy buffer (completely untested):

        copy_size_max = PAGESIZE;
        
        ebuf_start = round_down(off, 8);
        ebuf_length = min(count + 16, copy_size_max); // copy extra for alignment at start and end
        count = min(count, copy_size_max);  // Adjust for max copy
        length
        count = count - (off & 7); // Adjust for non aligned offset
        
        tbuff = __get_free_page(GFP_KERNEL);
        
        _memcpy_fromio(tbuff, ebuf_start, ebuf_length);
        memcpy(buf, tbuff + (off & 0x7), count); // grab what we need
        
        free_page(tbuff);
        
        return count;
        
Mikey

> +
> +	return count;
> +}
> +
>  static int cxl_init_afu(struct cxl *adapter, int slice, struct pci_dev *dev)
>  {
>  	struct cxl_afu *afu;
> diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c
> index d0c38c7..4942d55 100644
> --- a/drivers/misc/cxl/sysfs.c
> +++ b/drivers/misc/cxl/sysfs.c
> @@ -356,6 +356,16 @@ static ssize_t api_version_compatible_show(struct device *device,
>  	return scnprintf(buf, PAGE_SIZE, "%i\n", CXL_API_VERSION_COMPATIBLE);
>  }
>  
> +static ssize_t afu_eb_read(struct file *filp, struct kobject *kobj,
> +			       struct bin_attribute *bin_attr, char *buf,
> +			       loff_t off, size_t count)
> +{
> +	struct cxl_afu *afu = to_cxl_afu(container_of(kobj,
> +						      struct device, kobj));
> +
> +	return cxl_afu_read_err_buffer(afu, buf, off, count);
> +}
> +
>  static struct device_attribute afu_attrs[] = {
>  	__ATTR_RO(mmio_size),
>  	__ATTR_RO(irqs_min),
> @@ -534,6 +544,10 @@ void cxl_sysfs_afu_remove(struct cxl_afu *afu)
>  	struct afu_config_record *cr, *tmp;
>  	int i;
>  
> +	/* remove the err buffer bin attribute */
> +	if (afu->eb_len)
> +		device_remove_bin_file(&afu->dev, &afu->attr_eb);
> +
>  	for (i = 0; i < ARRAY_SIZE(afu_attrs); i++)
>  		device_remove_file(&afu->dev, &afu_attrs[i]);
>  
> @@ -555,6 +569,22 @@ int cxl_sysfs_afu_add(struct cxl_afu *afu)
>  			goto err;
>  	}
>  
> +	/* conditionally create the add the binary file for error info buffer */
> +	if (afu->eb_len) {
> +		afu->attr_eb.attr.name = "afu_err_buff";
> +		afu->attr_eb.attr.mode = S_IRUGO;
> +		afu->attr_eb.size = afu->eb_len;
> +		afu->attr_eb.read = afu_eb_read;
> +
> +		rc = device_create_bin_file(&afu->dev, &afu->attr_eb);
> +		if (rc) {
> +			dev_err(&afu->dev,
> +				"Unable to create eb attr for the afu. Err(%d)\n",
> +				rc);
> +			goto err;
> +		}
> +	}
> +
>  	for (i = 0; i < afu->crs_num; i++) {
>  		cr = cxl_sysfs_afu_new_cr(afu, i);
>  		if (IS_ERR(cr)) {
> @@ -570,6 +600,9 @@ err1:
>  	cxl_sysfs_afu_remove(afu);
>  	return rc;
>  err:
> +	/* reset the eb_len as we havent created the bin attr */
> +	afu->eb_len = 0;
> +
>  	for (i--; i >= 0; i--)
>  		device_remove_file(&afu->dev, &afu_attrs[i]);
>  	return rc;