Messages in this thread | | | Date | Fri, 21 Apr 2023 22:27:49 +0530 | Subject | Re: [PATCH v4 5/5] spi: spi-qcom-qspi: Add DMA mode support | From | Vijaya Krishna Nivarthi <> |
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Hi,
Thanks a lot for the review and inputs...
On 4/20/2023 10:49 PM, Doug Anderson wrote: > Hi, > > On Thu, Apr 20, 2023 at 6:13 AM Vijaya Krishna Nivarthi > <quic_vnivarth@quicinc.com> wrote: >> @@ -137,11 +155,29 @@ enum qspi_clocks { >> QSPI_NUM_CLKS >> }; >> >> +enum qspi_xfer_mode { >> + QSPI_FIFO, >> + QSPI_DMA >> +}; >> + >> +/* >> + * Number of entries in sgt returned from spi framework that- >> + * will be supported. Can be modified as required. >> + * In practice, given max_dma_len is 64KB, the number of >> + * entries is not expected to exceed 1. >> + */ >> +#define QSPI_MAX_SG 5 > I actually wonder if this would be more nicely done just using a > linked list, which naturally mirrors how SGs work anyway. You'd add > "struct list_head" to the end of "struct qspi_cmd_desc" and just store > a pointer to the head in "struct qcom_qspi". > > For freeing, you can always get back the "virtual" address because > it's just the address of each node. You can always get back the > physical address because it's stored in "data_address". > Please note that in "struct qspi_cmd_desc"
data_address - dma_address of data buffer returned by spi framework
next_descriptor - dma_address of the next descriptor in chain
If we were to have a linked list of descriptors that we can parse and free, it would require 2 more fields
this_descriptor_dma - dma address of the current descriptor
next_descriptor_virt - virtual address of the next descriptor in chain
I tried adding same and it seemed like it was getting a little confusing.
Given the SGL is also an array in SGT, it seemed ok to retain an array, though it would have good to have a chain of cmd_descriptors in SW like in HW.
Agreed the fixed size array comes at a cost of artificial limitation of 5 entries, which anyway seems like something we are not going to encounter in practice.
So for now, I retained the array.
All the other comments are addressed as recommended, except 1 change below
Please let know what you think.
Thank you,
Vijay/
> >> +static int qcom_qspi_alloc_desc(struct qcom_qspi *ctrl, dma_addr_t dma_ptr, >> + uint32_t n_bytes) >> +{ >> + struct qspi_cmd_desc *virt_cmd_desc, *prev; >> + dma_addr_t dma_cmd_desc; >> + >> + /* allocate for dma cmd descriptor */ >> + virt_cmd_desc = (struct qspi_cmd_desc *)dma_pool_alloc(ctrl->dma_cmd_pool, >> + GFP_KERNEL, &dma_cmd_desc); > Remove unnecessary cast; "void *" assigns fine w/out a cast. > > Add "| GFP_ZERO" and then get rid of the need to clear the "reserved" > and "next_descriptor" stuff below. > I needed __GFP_ZERO to prevent a compile error, used same.
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